In a large mixing bowl, stir together the yellow cake mix, 4 ounces cream cheese (softened), the softened butter, vanilla extract, and the egg. Stir until well combined, into a soft dough. Cube the remaining (cold) cream cheese and fold in. Some may mix but you don't want the pieces to completely mix in, you want them to remain small cubes as much as possible.
Spoon onto a baking sheet lined with a baking mat or parchment paper. Bake at 325°F for 10-11 minutes. These should still be very soft in the center. Remove to a cooling rack and dust with powdered sugar.