Heat oven to 180C/fan 160C/gas 4. Butter a 900g/2lb loaf tin and line with a strip of baking paper, or use a loaf tin liner (see tip, below). Beat together the butter and sugar until pale and creamy, then beat in the eggs one by one. Grate half the apple and mix it into the batter with the vanilla, dried fruit and ground almonds. Mix the baking powder, flour and spices together with a pinch of salt, then fold into the mix until even. Spoon into the tin and level the top.
Thinly slice the remaining apple half, toss with the lemon or orange juice, poke the slices a little way into the batter, then sprinkle with 1 tsp more sugar. Bake for 45 mins, then turn the oven down to 140C/fan 120C/gas 1. Cover the cake with foil, then bake for another 45 mins until a skewer inserted into the middle comes out clean. Cool in the tin.
To finish the cake, melt the marmalade or jam in a small pan, sieve to remove any lumps, then brush it over the cake to glaze the top. Serve cut into thick slices, and spread with a little butter, if you like. Will freeze for up to 1 month.