Butter and line the base of two 20cm sandwich tins.

Coarsely grate two thirds of the chocolate and chop the rest.

Set aside.

2)Put the flour, baking powder and sugar into a large mixing bowl.

Make a well in the centre and add the butter, eggs and milk (the butter must be very soft for this to work).

Beat together with a hand held electric whisk for about 2 minutes until light and fluffy (or use a wooden spoon and beat well for 3 minutes).

Lightly fold in the grated, chopped chocolate and mashed banana.

3)Divide the mixture evenly between the tins.

Gently level the surface with the back of a metal spoon or spatula.

Bake side by side on the middle shelf for 25-30 minutes until springy to the touch and beginning to shrink away from the sides.