Preheat the oven to 160°C or 320°F. Spray a 20cm cake tin with neutral oil and line with parchment paper. In two separate bowls mix the grated apples and sliced apples with 1/2 tbsp of lemon juice each, and set aside.
In a mixer with a paddle attachment, cream the butter and sugar until they're smooth and pale. In a bowl, mix together the dry ingredients; flour cinnamon, ginger, nutmeg, salt and baking powder.
Slowly start adding, and alternating, the eggs, apple juice and flour until everything is incorporated. Lastly, add the grated apples and the chopped walnuts and combine.
Fill the cake tin with the cake mixture and decorate the top of the cake by placing the sliced apples in a circular pattern.
Bake the cake for about 50 minutes, or until a toothpick or skewer comes out clean once inserted in the middle of the cake.
Leave to cool in the pan for 5 minutes before transferring the cake to a cooling rack to finish cooling.