Preheat oven to 350°F. Line a muffin tin with liners; set aside.
Using an electric mixer, cream butter and sugar at medium-high speed until fluffy, about 3 minutes. Add eggs one at a time, beating after each. Mix in vanilla, baking powder and salt at low speed. Mix in half of flour; add milk and remaining flour; mix at low speed until smooth.
Spoon batter into prepared cups. Bake until a cake tester comes out clean, 20 minutes. Let pan cool.
Frost with buttercream and decorate as desired.