I followed the dough recipe exactly but decided to scale down the amount of toppings, which turned out just enough to coat the dozen buns.
Makes enough toppings for 12 buns
75g salted butter, at room temperature
60g icing sugar, sifted
60g eggs (about 1 egg)
4 tsp instant coffee powder dissolved in 0.75 tbsp water
75g plain flour, sifted
1) Add all the ingredients in the bowl of a stand mixer. Using the paddle attachment, cream the mixture until it is evenly mixed, light and fluffy.
2) Fill the topping in a pastry bag and pipe spirals on the proved buns.
Unfortunately, I over-proved the buns on the final proof, and they turned out kind of flat. That is a real pity as I am sure it would have tasted so much better otherwise. Oh well, that gives me an excuse to bake another batch sometime soon.