line a 9x13 inch baking pan with parchment and lightly grease.
Mix batter
whisk melted butter brown sugar and granulated sugar until smooth
whisk in eggs and vanilla
stir in flour oats cinnamon baking powder baking soda and salt just until combined
fold in raisins.
Add swirl
spread batter evenly in pan
whisk swirl ingredients and drizzle over batter then gently drag a knife through to marble.
Bake and finish
bake until edges are set and center springs back lightly 22 to 28 minutes
cool completely in pan then lift out and slice
whisk glaze ingredients and drizzle if using.
Notes
1. For thicker bars use a 9x9 inch pan and add 5 to 10 minutes bake time. Swap raisins with golden raisins dried cranberries or chopped dates. Do not overbake for best chewiness