Prepare a buttered and lined 8-inch (20 cm) square cake tin (approx. size). Cream the butter and sugar and stir in the potatoes. Add the melted chocolate and beat in with the eggs.
Sift the dry ingredients and stir in with the almonds and milk. Pour the mixture into the cake tin and bake at gas mark 5/375°F/190°C for 12 minutes, then turn down the heat to gas mark 4/350°F/180°C for a further 45–50 minutes. Allow to cool in the tin for 5 minutes before turning out.