Preheat oven and prepare tin:

Set oven to 350°F (175°C). Prepare a muffin tin by lining with paper liners or greasing lightly.

Whisk dry ingredients together:

In a medium bowl, whisk together flour, baking powder, and salt until blended.

Cream butter and sugar:

In a large bowl, beat softened butter and granulated sugar together until pale and fluffy.

Beat in eggs and vanilla:

Add eggs one at a time, beating well after each, then mix in vanilla extract until smooth.

Alternate flour and milk additions:

Alternately add the flour mixture and milk to the butter mixture, starting and ending with flour. Stir just until combined; avoid overmixing.

Fold in rainbow sprinkles:

Fold in rainbow sprinkles gently until evenly dispersed.

Fill muffin cups:

Divide batter among muffin cups, filling each about two-thirds full.

Bake until golden:

Bake for 18-20 minutes, until a toothpick inserted in the center comes out clean.

Cool in tin then rack:

Let muffins cool in the tin for 5 minutes, then transfer to a wire rack to cool completely.

Dust or frost as desired:

Dust with powdered sugar or spread cream cheese frosting on top as desired.