Preheat the oven to 350°F. In a small bowl, whisk together the flour, baking powder and salt. In a medium bowl, using a hand-held mixer on medium speed, beat together the butter and sugar until light. Beat in the eggs one at a time, mixing well between additions. Add vanilla and blend well. Gradually beat half of the dry ingredients into the butter mixture, then half of the sour cream; repeat with the remaining dry ingredients and sour cream.

Divide the batter evenly among the prepared muffin cups. Bake until the tops spring back when lightly tapped, 20–25 minutes. Cool on a wire rack for 10 minutes, then turn out the cupcakes and cool completely on the rack before decorating.

Once the cupcakes are cool, spread buttercream frosting evenly on top. Use flat white candy or halved marshmallows to add white spots.

In a medium bowl, use a hand-held mixer on medium speed to beat together the confectioners' sugar and butter until blended. Beat in the vanilla and enough of the cream to achieve a soft consistency suitable for spreading. For different colors of buttercream, divide it among small bowls, then add 1 or 2 drops of desired food coloring to each bowl and stir well to blend.