This is a coffee flavoured buttercream adapted from https://gfpatisserie.com/recipes/ermine-buttercream#/
It is perfect for those who love coffee and a not too sweet buttercream. A cooked flour pudding is added to well beaten butter and again beaten to give a very smooth frosting.
Ingredients
2 tablespoons instant coffee
1 cup granulated sugar (can reduce up to 2 tablespoons if needed)
4 tablespoons all purpose flour
A pinch of salt
1 cup milk
1 tsp vanilla extract
1 cup unsalted butter
Combine the dry ingredients in a thick bottomed pan. Slowly add the milk to bring the mix to a smooth consistency. Place over medium heat and bring to a boil stirring continuously to avoid it from sticking to the bottom. The pudding should thicken like the picture given below.
Take it off the heat and stir for some more time. Let the pudding cool completely (will become like thick glue) and mix in the vanilla.
Take the cold butter and cube it in the bowl of your mixer. Wait until it has softened a little..maybe 15 mins depending on the climate. You don't want it going all soft and spreading. It should be firm. Start beating the butter on medium speed till the colour has become very light. 
Add the cooled pudding a spoon at a time and beat well till it has combined into a smooth and fluffy cream.
This can fill and coat a 3 layer 8 inch cake.
