Preheat your oven - conventional 180°C, Fan assisted 160°C, Gas mark 5.
Beat your butter and sugar together until smooth, creamy and pale white. I should be fluffy in texture.
Slowly add your egg into the mix, about an egg's worth at a time, beating until combined. Don't worry if it looks a bit curdled.
Gently mix on the flour and cocoa powder and baking powder on slow or fold in with a spoon. Stir in your soured cream.
Pop in your muffin cases, fill just over half way and bake for approx 12-15 minutes, check after 10, all ovens vary, to check they are cooked, test with a metal skewer or sharp knife and this should come out clean.
Once cooked, turn out on a wire rack.
Now for the fun part, the chocolate topping! Melt your chocolate, butter, golden syrup and cream in a microwave safe bowl for a minute at a time on a low setting in the microwave so the chocolate doesn't burn, stir each time until your pouring Ganache is smooth and silky. You can do this the conventional way on the hob over a pan of simmering water of course.
The easiest way to top the cakes is to pour your chocolate into a jug with a lip and slowly trickle the chocolate onto the sponge, taking care not to over fill. Once you have what looks like almost enough, gently tap the cake case onto your surface by picking up and banging carefully, so the chocolate icing Ganache neatly covers the top. ET voila! Ooh I can taste it now, once set for a couple of yours you can go crazy with your toppings, there are loads of options in the supermarkets now including gold chocolate buttons, readymade iced flowers glitters, sprinkles or if you feel adventurous, try making your own decoration with some sugar paste, available in supermarkets too.