For cake:

Preheat oven to 325 degrees

In an electric mixer, beat eggs and sour cream.

In another bowl, combine flour, sugar, baking soda, and salt.

Combine coffee stout and butter in a small saucepan and heat until butter melts. Remove from heat and whisk in cocoa powder.

While mixer is running, slowly pour in hot cocoa/butter mixture. Mix until fully incorporated.

Slowly add dry goods to wet and beat until incorporated. Fill lined cupcake tins 2/3 with batter.

Bake for 10 minutes and let cool on a cooling rack.

For filling:

Simmer cream over medium heat until just bubbling. Take care not to boil over.

Meanwhile, chop the milk chocolate into chunks and transfer into a bowl.

When cream is heated pour over room temperature chocolate.

Let chocolate and cream mixture sit for a minute or so, and then whisk. When smooth, add the butter. Ganache should be glossy.

While whisking, stream in port until incorporated.

For frosting:

In an electric mixer, beat butter with paddle until fluffy.

On low speed, add the powdered sugar.

Slowly stream in espresso and beat until smooth.

Stir in espresso powder and transfer to a piping bag.

Assembly:

When cupcakes are cool, use a small pastry tip to core out the center.

Fill the cupcakes with the port ganache, using a squeeze bottle.

Frost the cupcakes to your liking.