In a large mixing bowl cream together the butter and sugar until fluffy, about 3–4 minutes.

Add vanilla and beat again.

Add eggs one at a time, beating well after each addition.

In a separate bowl, mix together flour, baking powder, and salt.

Alternate adding the flour mixture and buttermilk to the creamed mixture in 3 batches, starting and ending with dry ingredients. Beat after each addition just until combined.

Line a lightly greased muffin pan with cupcake liners and fill each liner ¾ of the way full.

Bake in a preheated 350°F (175°C) oven for 18-25 minutes, or until a toothpick comes out clean.

Allow cupcakes to cool completely.

In a medium bowl, beat egg yolks well and gradually stir in milk until well blended.

In a large saucepan over medium-low heat, mix together sugar, cornstarch, and salt.

Gradually add the milk mixture, stirring well to prevent lumps.

Continue cooking over medium-low heat, stirring constantly until the mixture reaches a low boil, approximately 20 minutes.

Remove from heat and set pot in a bowl of ice water, continuing to stir.

Add vanilla and stir to combine. Cover with plastic wrap directly on the surface and refrigerate until ready to use.

Place chocolate in a food processor and process until finely chopped.

Heat cream in a small saucepan until steaming, then gradually add to the chopped chocolate, whisking until smooth.

Let it cool until manageable but not hardened.

Once cupcakes are completely cool, fill a piping bag with the pastry cream.

Fill each cupcake with pastry cream and place aside.

Dip each cupcake into the cooled ganache and allow 30 minutes to an hour for it to set.