Rhubarb Coffee Cake Bars are my kind of spring baking: a buttery crust, a soft coffee-cake middle, and a crumbly cinnamon streusel on top. They’re sweet-tart in that rhubarb way that keeps you going back for another small square.
The filling bakes up jammy and bright, and the sour cream in the batter keeps the cake layer tender. I like the little bit of oats in the topping too—it makes the crumble feel more like a true coffee cake than a plain crumb bar.
For me, these are best for weekend breakfasts, brunch tables, and those afternoons when you want something nice with coffee but don’t want to fuss with a layer cake.
Why You’ll Love This Recipe
Real coffee-cake vibes: You get the buttery base, the soft cake, and that thick cinnamon streusel in every slice.
Rhubarb front and center: The filling stays tangy and bright, and it cuts through the richness in a really nice way.
Easy to slice and share: A 9×13 pan makes tidy bars for bake sales, brunch, and potlucks.
Make it your way: Add orange zest, swap in a little strawberry, or toss pecans into the streusel depending on what you’ve got.
That crumble topping: The oat streusel bakes up crisp on top and a little buttery underneath where it meets the fruit.
Ingredients You’ll Need
Pan and base batter
- All-purpose flour: I use regular flour here. It keeps the base sturdy enough to hold the fruit layer without getting cakey in a weird way.
- Granulated sugar: Plain white sugar is what I reach for in the base so the rhubarb still tastes bright.
- Baking powder: This gives the cake layer its lift. Make sure yours is fresh, especially if it’s been sitting in the pantry for a while.
- Fine salt: Don’t skip it. It keeps the crust and streusel from tasting flat.
- Unsalted butter: Cold butter is key for that crumbly, press-in base. I like unsalted so I can control the salt level.
- Egg: One egg helps bind the batter and gives the cake layer some structure.
- Sour cream: This is what keeps these bars tender and a little rich. Full-fat Greek yogurt works the same way if that’s what you have.
- Vanilla extract: Just enough to round out the flavor. I keep it simple and use regular vanilla.
- Nonstick spray: Even with parchment, I still give the pan a light spray so the corners lift out cleanly.
Rhubarb filling
- Rhubarb: Fresh is great, but frozen works too—just thaw and drain it well so the bars don’t bake up soggy.
- Granulated sugar: Rhubarb needs a little help. If your stalks are especially tart, you can lean a touch heavier with the sugar.
- Cornstarch: This thickens the fruit juices as it bakes so the filling sets instead of running all over the place.
- Ground cinnamon: A small amount warms up the filling and ties it to the streusel on top.
- Orange zest (optional): I like it when I have an orange around. It makes the rhubarb taste a little brighter.
Streusel topping
- All-purpose flour: This keeps the streusel clumpy and crumbly instead of melting into the fruit.
- Light brown sugar: Brown sugar is the classic coffee-cake flavor here. Dark brown sugar works too if you want a deeper molasses note.
- Old fashioned oats: I like old fashioned oats for texture. Quick oats work in a pinch, but the topping is a bit less chunky.
- Ground cinnamon: This is the main flavor in the crumble, so use a cinnamon you actually like.
- Unsalted butter: Melted butter makes the streusel fast and reliable. Stir until you get nice clumps.
- Fine salt: A little salt keeps the streusel from tasting overly sweet.
- Chopped pecans (optional): I add them when I want crunch. Walnuts work too, or leave the nuts out completely.
Glaze (optional)
- Powdered sugar: This gives you that thin, classic drizzle that sets up nicely once chilled.
- Milk: Add just enough to get a drizzly consistency. Any milk you keep in the fridge is fine.
- Vanilla extract: A small splash makes the glaze taste finished instead of just sweet.
Recipe Instructions
- Preheat the oven: Heat the oven to 350°F. Line a 9×13-inch pan with parchment paper, then lightly grease it with nonstick spray.
- Mix the dry ingredients: In a large bowl, whisk together the flour, granulated sugar, baking powder, and salt.
- Cut in the butter: Add the cold, cubed butter and cut it into the dry ingredients until the mixture looks crumbly with small buttery pieces.
- Add the wet ingredients: Stir in the egg, sour cream, and vanilla just until the dough comes together. Don’t overmix.
- Press in the base: Press about two thirds of the mixture firmly into the prepared pan in an even layer.
- Mix the rhubarb filling: Toss the diced rhubarb with the sugar, cornstarch, cinnamon, and orange zest (if using), then spread it evenly over the base.
- Make the streusel: In a bowl, mix the streusel flour, brown sugar, oats, cinnamon, and salt. Stir in the melted butter (and pecans if using) until the mixture forms clumps.
- Add the topping: Crumble the streusel evenly over the rhubarb layer.
- Bake: Bake for about 38 to 45 minutes, until the top is golden and the cake portion tests clean with a toothpick.
- Cool: Cool completely in the pan before slicing so the filling can set.
- Glaze and slice: Whisk the powdered sugar, milk, and vanilla for the glaze and drizzle over the cooled bars if you want. Chill for about 15 minutes to set the glaze, then slice into squares.
Some of my tips!
This is the part that really makes a difference. If you only read one section, make it this one because this is where I share the little trick that helps the recipe turn out so well.
Recipe Tips & Tricks
Use parchment paper. These bars are much easier to lift and slice when you can pull the whole slab out of the pan. I still like a light spray under and over the parchment for the corners.
Drain frozen rhubarb really well. Frozen rhubarb is totally fine, but the extra water can make the base a little soft. I let it thaw in a colander and press out any extra liquid before mixing the filling.
Press the base in firmly. Take a minute to really pack it down, especially around the edges. A loose base tends to crumble when you cut the bars.
Don’t overbake the cake layer. You want a clean tester in the cake portion, but not a dry one. If the top is nicely golden, start checking sooner rather than later.
Chill before slicing. If you want neat, sharp squares, chill the pan and wipe your knife between cuts. The streusel stays put and the filling cuts cleaner.
Make some touches!
There are plenty of easy ways to serve this depending on the occasion. Keep it simple, or add a few small touches to make it feel a little more special.
Serving Suggestions
- Coffee or espresso: This is one of those bars that really does belong next to a mug of coffee. I like it best with a simple latte or black coffee.
- Whipped cream: A small dollop on the side is nice if you’re serving these as dessert. It’s also a good move if your rhubarb is extra tart.
- Ice cream: Vanilla ice cream with a slightly warm bar is great. If you’re into it, cinnamon or caramel ice cream is good here too.
- Fresh fruit: Strawberries, raspberries, or orange slices make the plate look a little brighter. I usually do this for brunch.
Save it for later
This section covers how to store leftovers and what parts of the recipe you can prepare ahead of time.
Storage and Make Ahead
Store leftovers covered in the fridge for up to 4 days. These bars hold together best when they’re chilled. You can eat them cold, or let a piece sit out for a bit to take the chill off.
If you want to make this recipe ahead, I usually bake the bars the day before and glaze them right before serving. The topping stays crisp, and the filling has time to set.
For longer storage, you can freeze individual portions in an airtight container. Thaw in the fridge overnight, and add the glaze after thawing if you want it to look neat.
If you like them warm, a quick microwave warm-up works fine. Just keep it short so the streusel doesn’t go soft.
A few quick answers
This section covers a few extra details that may help before you head to the recipe card.
Recipe FAQs
Can I use frozen rhubarb?
Yes. Thaw it first and drain it really well so you’re not adding a lot of extra liquid to the filling.
Can I add strawberries?
You can, and it’s really good. Replace up to about a third of the rhubarb with diced strawberries if you want the filling a little sweeter and less sharp.
Can I swap the sour cream?
Full-fat Greek yogurt works well and bakes up very similar. I wouldn’t use fat-free here because the texture can turn a bit dry.
How do I know when the bars are done?
The top should be golden, and a toothpick should come out clean when you test the cake portion (not the rhubarb filling). If the center still looks very loose, give it a few more minutes and check again.
Do I have to glaze them?
No, the glaze is optional. I like it for looks on a brunch table, but the bars are just as good without it.
You might also like
Before you go, take a look at a few other recipes below the recipe card. They use similar ingredients in a different way and are worth saving too.
MORE DINNER RECIPES TO TRY
Rhubarb Coffee Cake Bars
INGREDIENTS
Pan and base batter
- 2 cups all purpose flour
- 1 cup granulated sugar
- 2 tsp baking powder
- ½ tsp fine salt
- ¾ cup unsalted butter cold and cubed
- 1 large egg
- ½ cup sour cream
- 1 tsp vanilla extract
- nonstick spray.
Rhubarb filling
- 3 cups rhubarb diced
- ½ cup granulated sugar
- 2 tbsp cornstarch
- ½ tsp ground cinnamon
- 1 tbsp orange zest optional.
Streusel topping
- ¾ cup all purpose flour
- ¾ cup light brown sugar packed
- ½ cup old fashioned oats
- ½ tsp ground cinnamon
- ½ cup unsalted butter melted
- ¼ tsp fine salt
- ½ cup chopped pecans optional.
Glaze optional
- ½ cup powdered sugar
- 1 tbsp milk
- ½ tsp vanilla extract.
INSTRUCTIONS
Prep and bake
- heat oven to 350 F and line a 9x13 inch pan with parchment then lightly grease
- whisk flour sugar baking powder and salt then cut in cold butter until crumbly
- stir in egg sour cream and vanilla just until combined and press about two thirds of the mixture firmly into the pan
- toss rhubarb with sugar cornstarch cinnamon and orange zest then spread evenly over the base
- combine streusel flour brown sugar oats cinnamon and salt then stir in melted butter and pecans until clumpy
- crumble streusel evenly over rhubarb and bake until golden and set with a clean tester in the cake portion about 38 to 45 minutes.
Cool and finish
- cool completely in pan for clean slices
- whisk glaze ingredients and drizzle over cooled bars if using then chill 15 minutes to set and slice.
