Preheat the oven to 170°C bake and line a cupcake tray with 12 cupcake cases. Set aside.

In a medium sized saucepan, add in the beer and first measure of butter. Stir on a low heat until melted and combined. Do not boil.

Remove the saucepan from the heat, then whisk in the cocoa powder and sugar until dissolved. Allow to cool slightly.

Using a free-standing mixer or hand-held beater, beat together the egg, sour cream and vanilla in a separate bowl until combined.

Slowly pour the beer and butter mixture in with the egg, while still beating on a low speed. When combined, add in the flour and baking soda and continue to beat until smooth.

Transfer mixture to a small jug and pour into prepared cupcake cases, filling to about ⅔ full.

Bake for around 16-20 minutes or until a toothpick comes out clean and cupcakes spring back when touched. Remove from the oven and allow to cool.

For the buttercream, add the butter and cream cheese to the bowl of a free-standing mixer or using a hand-held beater, and beat for about 2-3 minutes until well combined.

Add the icing sugar in two stages, beating for another 3 minutes between each addition. If the buttercream is still quite firm, beat in small amounts of milk until desired consistency is reached.

Pipe blobs of buttercream on top of cooled cupcakes and decorated with pretzels. You can either roll the top of the cupcake in a saucer of broken pretzel pieces or spend some time arranging pretzels on top by hand. Enjoy!