Line cupcake pan with liners or grease pan with butter and lightly dust with flour. Melt butter and add eggs one at a time, then stir in vanilla.
In another bowl, sift together flour, baking powder, baking soda, cocoa powder, sugar and salt and add flour mixture with milk to the butter mixture. Fill cupcake cups half full.
Preheat oven to 350°F and bake for 15–17 minutes, or until the toothpick inserted into cupcakes comes out clean.
Remove from oven and let cool for a few minutes before transferring to a wire rack. Allow cupcakes to cool completely before frosting.
For the frosting: combine butter, sugar, cocoa powder and salt and beat with electric mixer until blended. Add the milk, vanilla and beat for 5 minutes or until it reaches a smooth and creamy consistency. Spoon frosting into piping bag with French tip and pipe frosting directly onto cupcake. Optional: sprinkle sparkling sugar on top of frosting.
For the decorations: roll out light pink fondant and cut out a heart shape. Roll out two tiny pieces of black fondant for the eyes and glue to the heart-shaped fondant using water. Roll out a tiny piece of pink fondant and glue it to the bottom of the heart-shaped ivory fondant. Place fondant on top of cupcake.