• Preheat oven to 150C/300F  or 130C/265F fanforced. Grease a 22 cm / 9" cake pan and line with parchment / baking paper. 
• Place butter and chocolate in a heatproof bowl and microwave for 30 sec. Give it a stir and put it in again for 30 sec, stir again. The chocolate should melt while being mixed. If its still not, put it in again for 30 sec.
• Add sugar into the chocolate mixture and mix. Add the egg and mix until combined well.
• Sift cocoa powder, baking powder and flour directly into the bowl using the sieve. Add hot water and mix until its all well combined. And batter will be bit runny.
• Pour the batter into the prepared tin and place it in the oven. The cake should be ready in 50 to 60 minutes. Insert skewer and it should come out clean but moist.
• Allow the cake to cool down completely on a wire rack.

Chocolate Ganache

• Add cream and chocolate in bowl. And microwave for 1 minute. Don't let the cream boil it should be hot enough to melt the chocolate when stirred with spatula. Alternatively you can also use double boiler method to melt chocolate and cream.
• Mix the chocolate and cream well, at this stage it will be runny. Cover the bowl and refrigerate for at least 2 hours.
• After refrigerating the ganache will become thick and spreadable. It will have peanut butter like consistency.
• Spread it over cooled cake. Serve it as is or decorate with your choice of decorations ( Berries, Sprinkles, chocolate shavings etc.)