To prepare a too cool for school pumpkin spice cake recipe, first you need to gather your ingredients. First, you'll need the following ingredients: 12 cup pumpkin puree, 1 tablespoon pumpkin pie spice, 1/2 teaspoon vanilla extract, and 1 teaspoon cinnamon. Mix all of the ingredients together until they're well combined. Pour the batter into the prepared cake pan. Bake the cake for 35 to 40 minutes, or until the toothpick inserted in the center comes out clean. Let cool before cutting into squares.