Ingredients
Method
- Heat oven to 350°F (177°C) and line a 9x9-inch pan with parchment.
- Whisk butter and brown sugar, then eggs and vanilla.
- Stir in flour, cream of tartar and baking soda.
- Spread in the pan and sprinkle with cinnamon sugar.
- Bake 23–26 minutes. Cool completely before cutting.
