Preheat the oven to 180'C.
Zest the juice the lemon. Peel, core and cut the apples into 1cm pieces and mix with the lemon juice.
Grease a deep 24cm springform cake tin with butter and line with baking paper.
Cream the butter, caster sugar and lemon zest in a bowl until pale and fluffy. Beat in the eggs, 1 at a time, adding a little flour with each egg to keep the mixture smooth.
Sift in the remaining flour and the baking powder and fold in the ground almonds. Drain the apple pieces well, then stir into the mixture.
Spoon into the prepared cake tin, level the top and sprinkle with the demerara sugar.
Bake in the oven for 1 hour or until well-risen, golden brown and a skewer inserted into the centre of the cake comes out clean.
Allow the cake to cool in the tin for 10 minutes and then place on a cooling rack. Dredge heavily with the extra caster sugar and serve with some clotted cream.
«Try using pears instead of apples, or even caramalising some apples to put on top of the cake to garnish.»