Preheat oven to 350°F. Line an 8x8-inch baking pan with parchment paper. Leave the sides a little higher than the pan so the bars can be lifted out easily after they’ve cooled. Spray the parchment paper lined pan with nonstick spray and set aside.
In a large bowl, using a hand mixer, beat the dry cake mix, butter, egg, vanilla extract, cinnamon, and nutmeg together until fully combined, about 30 seconds. Do not overmix.
15.25 ounces carrot cake mix, ½ cup unsalted butter, 1 large egg, 1 teaspoon pure vanilla extract, 1 teaspoon ground cinnamon, ¼ teaspoon ground nutmeg
In a separate medium bowl, beat the cream cheese on high until smooth, about 30 seconds.
4 ounces full-fat block-style cream cheese
Beat the sweetened condensed milk into the cream cheese until smooth, about 30 seconds. Set aside.
½ cup sweetened condensed milk
Press about ⅔ of the dough mixture into the bottom of the prepared pan. This dough will be thick (cookie dough consistency). If having difficulties spreading the dough into the pan, lightly spray a spatula with nonstick spray to help spread out the bottom layer.
Spread the cream cheese and sweetened condensed milk mixture evenly over the first dough layer.
Press the remaining ⅓ of the dough into super flat pieces and cover as much of the cream cheese and sweetened condensed milk layer with the dough as possible. It’s okay if some of the cheesecake layer is still exposed.
Bake for 29-31 minutes – the middle will look set and the edges will be slightly browned. Do not overbake or these bars will lose the gooey texture.
Let bars cool in pan for at least 60 minutes before removing from pan and slicing into 16 squares.