Heat the butter in a pan. Add the apples, sugar and cinnamon, cover and cook for approx. 5 mins. Remove the pan from the heat.
Place the butter in a bowl. Add the sugar and salt, mix using the whisk on a hand mixer. Add the eggs one at a time and continue to whisk until the mixture becomes lighter in colour. Mix in the lemon zest and juice. Combine the flour, baking powder and cinnamon, mix in and transfer to the prepared tin. Top with the slices of apple and resulting juice.
Mix the nuts, sugar, butter and cinnamon until the mixture turns crumbly, scatter over the top.
Bake for approx. 50 mins. in the lower half of an oven preheated to 180°C.
Remove from the oven, allow to cool slightly, remove from the tin, place on a cooling rack and allow to cool completely. Dust with icing sugar.