Grease and flour a fairly deep 7 in (18 cm) sandwich tin. Put a disc of greaseproof paper in the bottom. Cream the butter and sugar and the vanilla essence in a bowl until light and fluffy. Add the eggs and the ground almonds alternately. Beat well. Dust the peel with a little flour and stir lightly into the mixture. Fold in the flour with a metal spoon. Turn mixture into the tin, smooth top and sprinkle with demerara sugar. Bake in the centre of a pre-heated oven Gas 4 (350°F/180°C) for 45–50 minutes. Cool in the tin before turning out – if necessary loosen sides with a knife. I usually stick a few flaked almonds into the top of the cake to decorate.