Make cake mix according to recipe on back of box except use only 2 eggs and 1 egg yolk rather than 3 full eggs.
For filling, unwrap 8oz pkg of cream cheese and microwave in microwave-safe bowl for 40 seconds. Stir in ⅓ cup + 1 Tbsp powdered sugar. Add in vanilla and stir.
Grease a mini-cupcake tin or line with paper liners. Layer bottom of cup with about 1 Tbsp cake mixture, then about 1-2 tsp cream cheese mixture, then top with cake mixture.
Bake in oven for 12-15 minutes or until toothpick inserted in top cupcake layer comes out clean.
Cool 5 minutes in cupcake tins and then move to rack. Sprinkle with remaining powdered sugar. Cool completely before serving.