Preheat oven to 350 degrees. Place cupcake liners in a cupcake tin.
Use a mixer to cream together butter and sugar until fluffy. Beat in eggs one at a time. Scrape down the sides of the bowl after adding each egg. Beat in the vanilla.
Sift together flour, baking powder, salt and cocoa powder. Beat half of the flour mixture into the wet mixture.
Beat in half of the milk. Beat in remaining dry ingredients. Beat in the rest of the milk. Beat in the boiling water.
Fill cupcake tins 2/3 of the way full.
Bake for 15 - 20 minutes or until a toothpick inserted comes out with a few crumbs on it. Allow cupcakes to cool for a few minutes in the tin.
Transfer cupcakes to a cooling rack to cool completely.
Once the cupcakes are cool, make the ganache by heating the heavy cream in a saucepan just until simmering. Place the chocolate chips in a bowl you can easily pour from (I used my 4 cup measuring cup). Pour the hot cream over the top. Make sure all of the chocolate is submerged in the cream. Let stand for two minutes.
Gently whisk the chocolate and cream together until the chocolate has melted and the mixture has a glossy look to it.
Spoon the ganache over the top of the cooled cupcakes. Sprinkle with sprinkles if using. Once the ganache hardens, serve.