Preheat the oven to 180 degrees C (fan) (or 200 degrees C conventional).
Grease and line two 20 cm cake tins (I use springform pans).
Mix the flour, baking powder and cocoa powder in a large bowl.
Place the butter and light brown sugar in a microwaveable dish. Microwave on high for 1 minute or until melted. Stir well. Allow to cool for a few minutes.
Add the milk to the melted butter and sugar mixture and whisk until smooth.
Pour the liquid mixture into the large bowl with the dry ingredients. Fold together gently.
Then add the beaten egg in thirds, mixing after each addition.
Pour the cake batter into the lined cake tins, splitting the mixture evenly between the tins.
Place the tins in the preheated oven, if you wish on a baking tray to keep them stable.
Bake for 20 to 25 minutes until a cake tester or toothpick comes out clean from the centre.
Remove the tins from the oven, leave to cool for five minutes or so until you can handle them. then push the cakes out of the springform pans by pushing up the base. Remove the base from under the cakes, peel off the baking paper and put them on a cooling rack.
Allow to cool completey.