Preheat your oven to 350 degrees Fahrenheit.
Afterward, take your 8x8 inch baking pan. And then, ensure to line it with parchment paper. After that, set it aside.
Using an electric mixer, take a large mixing bowl. Then, combine your sugar, milk, sour cream, egg, melted butter, and vanilla extract. Beat until everything combines well.
Next, add your pancake mix and gently fold it into the mixture using a rubber spatula. With that, make sure to fold until the dry mixture disappears.
Once finished with the cake batter, pour it into your prepared 8x8 inch baking pan lined with parchment paper. Afterward, place your cake inside the oven and bake it for about 20 minutes. Or bake it until thoroughly cooked. As a result, the cake will become slightly golden.
Finally, once the vanilla cake cooks entirely, ensure to let it cool over the counter. Likewise, you can cool it on a wire rack. Then, set it aside for frosting.