Chocolate pretzel nests

For the buns:

225g soft butter

220g golden caster sugar

210g self-raising flour

1 tsp vanilla

15g cocoa powder

For the chocolate pretzel nests:

100g dark chocolate, broken into small even-sized pieces

45g thin salted pretzels, broken into sticks

For the buttercream:

75g soft butter

100g icing sugar

50g cocoa powder

1 tsp vanilla

1 tbsp milk