To make cupcakes: Preheat oven to 350 F. Line 12-cup muffin tin with cupcake liners.
In bowl of electric mixer, sift flour, sugar, cocoa powder, baking soda, baking powder and salt.
In medium bowl, whisk egg, buttermilk, water, vegetable oil and vanilla extract.
Mix dry ingredients on low speed 1 minute. Add wet ingredients. Mix 2 minutes on medium speed and scrape sides and bottom of bowl. Mix 1 minute on medium speed.
Divide evenly among cupcake liners.
Bake 12-15 minutes, or until toothpick inserted in center comes out almost clean.
Cool cupcakes on wire rack.
To make frosting: Using paddle attachment of electric mixer, whip butter 8 minutes on medium speed until pale and creamy. Add powdered sugar, milk, vanilla extract and salt; mix on low speed 1 minute. Increase speed to medium and mix 6 minutes until frosting is light, creamy and fluffy. Add food coloring and whip 1 minute.
Pipe frosting onto cupcakes and top with egg-shaped chocolate-coated candies.