Preheat your oven to 180 C and line a 6 cup muffin pan.

Melt the butter and chocolate in the microwave or a double boiler and set aside to come to room temperature.

In the bowl of a stand mixer with the whisk attachment add the egg and the sugar and beat for 4 minutes on high speed till the mixture is light and fluffy. The sugar should dissolve in this step. Add the coffee and vanilla and mix well.

Now add the melted butter-chocolate mixture into the bowl and mix until combined.

Using an ice-cream scoop, portion out the batter to the muffin cups and top with chopped nuts/chocolates/candies etc if you like.

Bake for roughly 20-25 minutes. I usually bake for 20 because I prefer the texture it gives then. Let the muffins cool completely before consuming.