Rhubarb Coffee Cake Bars are buttery, thick bars with a tart rhubarb layer tucked between a soft cake base and a cinnamon streusel top. They eat like coffee cake, but they slice neatly and travel well.
I like that this version has a real crumbly base (not a cakey sheet cake) and the rhubarb stays bright and jammy instead of turning into a watery layer. The sour cream makes the dough tender, and the streusel gives you that classic coffee cake bite.
For me, these are best for weekend baking, spring potlucks, and anything brunch-y where you want a dessert that’s easy to cut and serve. They’re also great with an extra spoon of glaze if you like a sweeter finish.
Why You’ll Love This Recipe
Coffee cake in bar form: You get the same buttery, cinnamon-crumb thing, but it’s simpler to slice and serve.
Tart rhubarb layer: The rhubarb stays punchy and a little tangy, which keeps the whole pan from tasting flat.
That streusel top: The brown sugar and cinnamon bake into crisp little clumps that make these hard to stop nibbling.
Make-ahead friendly: These actually cut better after they’ve cooled and had a little time to set up.
Easy swaps: Greek yogurt works fine in place of sour cream, and frozen rhubarb is totally doable when fresh isn’t around.
Ingredients You’ll Need
Rhubarb Filling
- Rhubarb: Fresh is great, but frozen works too. If you’re using frozen, keep it frozen when you mix it so it doesn’t dump extra liquid right away.
- Granulated sugar: Rhubarb needs it. If your rhubarb is extra tart, you can lean a little heavier on the sugar, but I usually stick with the recipe as written.
- Cornstarch: This is what keeps the filling from turning runny in the pan. It thickens more as the bars cool.
- Lemon juice: Brightens the rhubarb and helps it taste a little fresher.
- Vanilla extract: Just enough to round out the tartness.
- Salt: Don’t skip the pinch. It keeps the filling from tasting sharp.
Cake Base
- All-purpose flour: I use regular flour here. Spoon and level if you tend to over-pack your measuring cup.
- Granulated sugar: Sweetens the base and helps it brown a bit around the edges.
- Baking powder: Gives the base a little lift so it’s not too dense.
- Baking soda: Works with the sour cream for tenderness and a softer crumb.
- Fine salt: Makes the butter and vanilla taste more like themselves.
- Unsalted butter: Cold butter is important for that crumbly, coffee-cake texture. I cut it small so it blends in faster.
- Sour cream: This is what makes the base tender and rich. Greek yogurt is fine if that’s what you have.
- Egg: Helps bind everything so the bars slice cleanly.
- Vanilla extract: Simple, classic, and it works especially well with rhubarb.
Streusel Topping
- All-purpose flour: Just enough to turn the butter and sugar into clumps.
- Brown sugar: I like packed light brown sugar here, but dark brown sugar works too if you want a deeper molasses note.
- Ground cinnamon: This is the coffee cake flavor. If your cinnamon is old, replace it—makes a difference.
- Fine salt: A little bit keeps the streusel from tasting overly sweet.
- Unsalted butter: Melted butter makes the streusel easy and reliably clumpy.
Optional Glaze
- Powdered sugar: Gives you that classic thin drizzle that sets up after a few minutes.
- Milk: Start small and add a touch more if you want it looser.
- Vanilla extract: Makes the glaze taste like more than just sugar.
Recipe Instructions
- Preheat the oven: Heat the oven to 350°F. Line a 9×13-inch pan with parchment paper, leaving an overhang, then lightly grease it.
- Mix the filling: Stir the diced rhubarb, sugar, cornstarch, lemon juice, vanilla, and a pinch of salt together in a bowl until everything looks evenly coated. Set aside.
- Mix the dry ingredients: In a large bowl, whisk together the flour, sugar, baking powder, baking soda, and salt.
- Cut in the butter: Add the cold, cubed butter and cut it into the flour mixture until you have pea-sized crumbs.
- Add the wet ingredients: In a small bowl, whisk the sour cream, egg, and vanilla. Stir it into the crumb mixture just until a thick dough forms.
- Press the base: Press about two-thirds of the dough into the prepared pan in an even layer.
- Add the rhubarb: Spread the rhubarb mixture evenly over the base.
- Add the top dough: Crumble the remaining dough over the rhubarb layer.
- Make the streusel: Stir the flour, brown sugar, cinnamon, salt, and melted butter together until clumpy.
- Top and bake: Sprinkle the streusel evenly over the top. Bake for 38 to 45 minutes, until golden and set in the center.
- Cool and slice: Cool completely, then lift out using the parchment overhang and slice into bars.
- Add the glaze: If using, whisk powdered sugar, milk, and vanilla, then drizzle over the cooled bars.
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. The rhubarb layer can get a little sticky at the edges, and parchment makes the lift-and-slice part simple.
Keep the butter cold. If it starts to soften while you’re mixing, the dough gets more like batter and less like crumbs. Cold butter gives you that coffee-cake texture.
Cut the rhubarb fairly small. Big chunks can make the bars harder to slice cleanly and can leave pockets of extra juice.
Don’t rush the cooling. The filling thickens as it cools, so warm bars tend to look messy when you cut them.
Chill before slicing for cleaner cuts. Even 30 minutes in the fridge helps a lot, especially if your kitchen is warm.
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 tea: These are made for a mug of coffee. I like them with something simple like black coffee or an Earl Grey.
- Whipped cream: A small dollop on the side is nice if you’re serving these as dessert instead of brunch.
- Vanilla ice cream: If you warm a bar slightly, vanilla ice cream is really good with the tart rhubarb.
- Fresh berries: Strawberries or raspberries on the plate make it feel a little more springy. It’s also a nice way to serve smaller squares.
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 the bars airtight at room temperature for 1 day. After that, I move them to the fridge so the rhubarb layer stays firm and the streusel doesn’t get too soft.
Refrigerate up to 5 days. I usually eat them chilled or let a piece sit out for 10 to 15 minutes so it loses the fridge chill.
You can bake these a day ahead and glaze right before serving if you want them to look fresh. They slice more neatly the next day anyway.
If you want them longer-term, freeze individual portions in an airtight container. Thaw in the fridge overnight before serving.
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. Use it straight from frozen (don’t thaw), and add 1 extra teaspoon of cornstarch to help with the extra moisture.
Can I swap the sour cream?
Greek yogurt is an easy swap and works well here. I prefer full-fat if you have it, since it keeps the base tender.
How do I know when the bars are done?
The top should be golden and the center should look set, not jiggly. A toothpick won’t come out perfectly clean because of the filling, but you shouldn’t see wet dough.
Why did my bottom layer feel a little dense?
That usually happens if the dough gets overmixed after adding the sour cream mixture. Stir just until it comes together, then press it into the pan.
Do I have to add the glaze?
No. I like these plain for breakfast or brunch, and I add the glaze when I’m serving them as dessert or bringing them somewhere.
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
Rhubarb Filling
- 3 cups rhubarb diced
- ½ cup granulated sugar
- 1 tbsp cornstarch
- 1 tbsp lemon juice
- ½ tsp vanilla extract
- pinch salt.
Cake Base
- 2 cups all purpose flour
- 1 cup granulated sugar
- 1 tsp baking powder
- ½ tsp baking soda
- ½ tsp fine salt
- ¾ cup unsalted butter cold cubed
- 1 cup sour cream
- 1 large egg
- 1 tsp vanilla extract.
Streusel Topping
- ½ cup all purpose flour
- ½ cup brown sugar packed
- 1 tsp ground cinnamon
- ¼ tsp fine salt
- 4 tbsp unsalted butter melted.
Optional Glaze
- ½ cup powdered sugar
- 1 tbsp milk
- ½ tsp vanilla extract.
INSTRUCTIONS
Prep
- heat oven to 350 degrees F and line a 9x13 inch pan with parchment leaving overhang then lightly grease
- mix rhubarb filling ingredients in a bowl until evenly coated and set aside.
Base And Assemble
- whisk flour sugar baking powder baking soda and salt then cut in cold butter until pea sized crumbs form
- whisk sour cream egg and vanilla then stir into crumbs just until a thick dough forms
- press about two thirds of dough into the pan in an even layer
- spread rhubarb mixture evenly over base
- crumble remaining dough over rhubarb.
Streusel And Bake
- stir streusel ingredients until clumpy then sprinkle evenly over top
- bake until golden and set in the center about 38 to 45 minutes
- cool completely before lifting out and slicing into bars.
Glaze
- whisk glaze ingredients and drizzle over cooled bars if desired.
