In a medium mixing bowl, whisk together 1 (3.4oz.) box vanilla instant pudding mix, 1½ cups cold whole milk, and 1 cup sour cream until smooth, and the mixture begins to thicken. Set aside. Cut the 14 ounce store bought angel food cake into 1-inch cubes and then evenly layer half of the cubes into the bottom of the baking pan.
Store leftover cake in an airtight container in the refrigerator for up to 2 days. I find any longer than that, the cake starts to become soggy.