You don’t have to have a heart-shaped muffin tin to make fun heart-shaped muffins or cupcakes for Valentine’s Day.
Simply line a tin with paper liners, then drop a marble in between the tin and liner. (Balls of aluminum foil will also work.)
Carefully fill the liners to a little over 1/2 full (overfilling will cover the heart shape effect). Bake, remove from pan, remove marbles, cool, and frost.