Line a 9” square baking tin with non-stick parchment paper.

Melt the butter, dark chocolate and milk chocolate in a heatproof bowl for 1-2 minutes. Leave to the side to cool to room temperature.

Whisk the eggs and sugar for a few minutes using an electric hand whisk/stand mixer until pale and doubled in size. When you lift the whisk out of the mixture it should leave a trail for a couple of seconds before disappearing.

Pour the cooled chocolate mixture over the egg mixture and carefully fold.

Sieve the plain flour and cocoa powder on top of the chocolate/egg mixture and gently fold. Carefully fold in the chocolate chips.

Pour the mixture into the prepared tin and bake for 30-40 minutes, or until the mixture no longer wobbles when you gently shake the tin and a skewer comes out mostly clean.

Leave to cool in the tin. You can pop them in the fridge for a few hours for an extra fudgy texture. Cut into 16 and enjoy.