For the apple-walnut cake, beat the honey, butter, cinnamon and salt until fluffy. Add the eggs little by little until everything is nicely mixed. Sift flour with baking powder and stir into the butter mixture.
Spread the dough on a greased baking tray (32 cm x 23 cm). Peel and core the apple and cut into wedges. Sprinkle with lemon juice and let sit for about 10 minutes.
Then place on top of the cake batter. For the cake glaze, bring honey, butter, vanilla sugar and milk to a boil and simmer for 1/2 minute. Add chopped walnut kernels to the mixture and let cool slightly.
Spread the cake glaze on the apples and bake in a preheated oven at 200 degrees for about 10 minutes and bake at 180 degrees for about 40 minutes.