1. Preheat oven to 350° F. Lightly brush muffin makers with oil.
2. In a large bowl, whisk cake mix with eggs, milk, oil, and 2 tsp vanilla until just combined. If desired, fold in sprinkles (be careful not to overmix; the colours will bleed).
3. Divide batter evenly into pans, filling cavities about ⅔ full.
4. Bake for 15–18 min, or until toothpick comes out clean. Cool in pan 10 min; unmold.
5. To make icing, use an electric mixer to beat cream cheese with butter until smooth. Beat in remaining vanilla and icing sugar, one spoonful at a time, until smooth. Allow cupcakes to cool completely before spreading on icing.
