Ingredients
Method
- Parchment-line 8x8 pan; heat oven to 350F.
- Whisk flour, cream of tartar, baking soda, and salt in bowl.
- Stir melted butter and brown sugar; beat in egg, yolk, and vanilla.
- Fold in dry just until combined; press thick batter into pan.
- Mix topping sugar and cinnamon; sprinkle evenly over.
- Bake 23 to 25 minutes until edges golden and center just set; cool before cutting.
Notes
Underbake slightly for fudgy centers.