Gooey Cinnamon Squares

Soft Cookie Base:
8 tbsp (1 stick) butter, at room temperature
1½ cups all-purpose flour
1 tsp cream of tartar
½ tsp baking soda
¾ cup sugar
1 large egg
¼ cup milk

Cake Layer:
¼ cup light corn syrup
¼ cup whole milk
1 tbsp vanilla
12 tbsp (1½ sticks) butter, at room temperature
1 cup plus 2 tbsp sugar
1 large egg
1¼ cups all-purpose flour

Topping:
2 tbsp sugar
1½ tsp cinnamon

Preheat oven to 350 degrees. Line the bottom of a 9”x13” pan with at least 2-inch sides of parchment paper. Coat entire pan with a nonstick spray.

SOFT COOKIE BASE: Whisk the flour, cream of tartar, and baking soda in a medium bowl. In a large bowl, cream the butter and sugar until light and fluffy. Add the egg and milk, and beat until combined, scraping down bowl and beating for 10 seconds more. Beat in dry ingredients until just combined.

Dollop the base over the bottom of the prepared pan and spread it into an even layer with a spatula. Set aside.

CAKE LAYER: Whisk corn syrup, milk, and vanilla together in a small bowl and set aside. In a  large bowl, cream the butter and sugar until light and fluffy. Beat in the egg, scraping down sides of the bowl, and mix for 10  seconds more. Add ⅓ of the flour and mix, then ½  of vanilla mixture and mix. Repeat again, twice, until all of the flour has been mixed just until combined. Dollop over the base and spread carefully with spatula.

TOPPING:
Mix the sugar and cinnamon in a tiny dish and sprinkle evenly over the entire cake layer.

Bake 25 to 30 minutes until bronzed in top. The cake layer will rise and fall in the oven but will still be slightly gooey under the cinnamon crust when squares are done. Let cool completely on a rack, then cut into squares.