Preheat the oven to 350°F (177°C). Line a 9×13-inch (23×33 cm) baking dish with parchment paper, leaving an overhang on two sides for easy removal, or lightly grease the pan.
In a large mixing bowl, combine the yellow cake mix, 2 of the eggs, and the melted butter. Mix with a hand mixer on medium speed just until fully combined and thick. Transfer the mixture to the prepared baking dish and press it evenly into the bottom using a spatula. Set aside.
1 box yellow cake mix, 4 large eggs, ½ cup (113 g) butter
In a separate bowl, add the confectioners’ sugar, softened cream cheese, remaining 2 eggs, and butter extract. Mix with the hand mixer on medium speed until smooth and fully combined, scraping down the sides of the bowl as needed.
3½ cups (420 g) confectioners' sugar, 8 oz (227 g) full-fat cream cheese, 1 tsp (5 ml) butter extract
Pour the cream cheese mixture evenly over the cake base, spreading gently to the edges.
Bake for 35 to 40 minutes, until the top is lightly golden and a toothpick inserted near the center comes out clean. For a softer, gooier center, remove the cake closer to the 35-minute mark. For a more set texture with a thinner gooey layer, bake closer to 40 minutes.
Allow the cake to cool completely before slicing into squares. If desired, finish with a light dusting of confectioners’ sugar just before serving.