Step 1

Preheat the oven to 350°F. Line an 8x8-inch baking pan with parchment paper, leaving an overhang on the sides.

Step 2

In a large bowl, beat the butter with 1 cup of granulated sugar and the brown sugar with an electric mixer on medium speed until light and fluffy, 2-3 minutes. Beat in the eggs one at a time, then mix in the vanilla extract.

Step 3

In a separate bowl, whisk the flour, cornstarch, baking powder, cream of tartar, 1 teaspoon of cinnamon, and salt. Add the dry ingredients to the wet and mix gently by hand until just combined. Press the dough into the prepared pan.

Step 4

In a small bowl, mix the remaining 1/4 cup granulated sugar and 1 1/2 teaspoons of cinnamon. Sprinkle evenly over the dough in the pan.

Step 5

Bake on the center rack for 25-30 minutes, until the edges are lightly browned and a toothpick inserted into the center comes out mostly clean.

Step 6

Let the bars cool completely in the pan on a wire rack. Then, use the parchment paper to lift the bars out of the pan and slice them into squares. Enjoy!