Preheat the oven to 180°C (350°F/Gas 4). Grease the base and side of a 20cm (8inch) spring-form cake tin, and line the base with baking paper.
Cream the butter and sugar in a small bowl using electric beaters until light and fluffy. Beat in the lemon zest. Add the eggs gradually, beating thoroughly after each addition. Transfer the mixture to a large bowl. Using a metal spoon, fold in the sifted flours and cinnamon alternately with the milk. Stir until the mixture is just combined and almost smooth.
Spoon half the mixture into the tin, top with three-quarters of the apple, then the remaining cake mixture. Press the remaining apple around the edge of the top. Combine the mixed spice, extra sugar and flaked almonds and sprinkle over the top of the cake.
Bake for 1 hour, or until a skewer inserted into the centre of the cake comes out clean. Leave in the tin for 15 minutes, then turn out onto a wire rack to cool.