Instructions

1. Preheat the oven to 350ºF. Spray a 9×13-inch baking dish with nonstick cooking spray.
2. In a small bowl, combine the flour, baking powder, cinnamon, salt and cream of tartar.
3. In a large bowl, beat together the butter and both sugars until light and fluffy. Gradually beat in the eggs, one at a time, scraping the sides of the bowl as needed. Beat in the vanilla.
4. Add in the dry ingredients and beat on low until combined.
5. Make the cinnamon filling by combining the sugar and cinnamon in a small bowl.
6. Spoon half of the batter into the prepared pan. The batter will be pretty thick – use your hands if needed to spread the batter evenly in the pan. Sprinkle the cinnamon sugar filling mixture evenly over the batter. Drop teaspoon sized amounts of the remaining batter over the cinnamon sugar layer.
7. Bake in the preheated oven for 20-25 minutes, or until golden brown. Cool completely.
8. In a small bowl, combine the powdered sugar, 1 teaspoon of the milk and the vanilla. Whisk, and add more milk if needed to make a drizzling consistency.
9. Drizzle the glaze over the cooled bars.
10. Cut and serve.