Preheat your oven to 180C / 350F / Gas mark 4
Line your muffin tins with liners, or grease them lightly.
In a small bowl sieve the cocoa, flour, baking powder and salt together.
Give it all a gentle mix so everything is well combined then set aside.
In another large bowl or in a mixer cream the butter and sugar together until it is light and fluffy.
Add the eggs one at a time mixing between each addition.
Mix in the vanilla extract.
On a low speed if using a mixer add half the flour and mix it in. Then add the sour cream and mix until everything is well combined. Then add the remaining flour.
Spoon the mixture into your prepared tins / cases till they are almost full.
Bake in the centre of your oven for 20 to 25 minutes, checking once 20 minutes are up. As I mentioned before I have a slow oven but if yours is faster they won’t take longer than 20 minutes.
Take them out of the oven and allow them to sit in their tins for a few minutes then take them out and allow them to fully cool on a cooling rack.