Ingredients
Method
- Heat oven to 350F; parchment-line 9x9 pan.
- Whisk flour, cream of tartar, baking soda, and salt.
- Stir melted butter and brown sugar; beat in eggs and vanilla.
- Fold in dry just until combined; spread in pan.
- Sprinkle cinnamon sugar evenly over.
- Bake 22 to 25 minutes until top set and center just firm; cool before slicing.
Notes
Brown the butter first for a deeper, nuttier flavor.