Preheat oven to 350 degrees F. Spray a 10-inch by 15-inch by 1inch baking sheet with non-stick spray.
In a small bowl, mix the topping ingredients (granulated sugar and cinnamon) with a fork. Set aside.
1/3 cup granulated sugar, 1 teaspoon cinnamon
In a large bowl, using a hand electric mixer or in the bowl of a stand mixer fitted with paddle attachment, beat together the butter and sugar until smooth and fully combined.
1 cup (2 sticks) unsalted butter, 1 ½ cups granulated sugar
Add the eggs and vanilla extract; mix until combined. Set aside.
2 large eggs, 1 ½ teaspoon vanilla extract
In another large bowl, whisk the flour, cream of tartar, baking soda, and salt until combined.
3 cups all-purpose flour, 1 ½ teaspoon cream of tartar, 1 teaspoon baking soda, ½ teaspoon kosher salt
Add the flour mixture into the wet ingredients and mix until a soft dough has formed.
Place the dough onto the prepared baking sheet and evenly press it to the edges.
Sprinkle topping mixture evenly over the top of the dough. Press the cinnamon sugar mixture gently with your hand so the dough sticks to it. Bake for 20 minutes, until the edges start to brown, and the center no longer appears jiggly. Cool completely before cutting.
Cut into 24 bars. Store in an airtight container.