Preheat oven to 350°F
Grease the springform pan. Set aside.
Peel, core, and slice the apples into chunks. I started with 6 apples weighing close to 1 1/2 kilos (around 3 1/3 pounds) before peeling. The bigger the chunks the more firm the pieces will be after baking. Place the chunks in a bowl, and set aside briefly. In a Mixing bowl, beat the sugar and butter for 3 minutes. Add the lemon zest, beat another 30 seconds.
Add the eggs, one at a time, beat until they starts to combine with the butter. Scrape the bottom of the bowl,
Combine the baking powder and flour, then, with the mixer going on low, slowly add the flour to the butter/egg mix.
Now add the apples to the batter. You can do this by hand, but I just poured them into the mixing bowl with the beater on low. Just for a short mix until the batter spreads onto the apple chunks.
With a spatula, finish mixing the apples into the batter, then scrape it all into the prepared pan.Smooth the top with your spatula. Bake for 50 minutes at 350°F Around the 45 minute mark melt the butter and mix the cinnamon into the sugar. (The more cinnamon sugar you add the thicker and darker the crust on top.)
At 50 minutes, remove the cake briefly from the oven (shut the oven door to keep the heat in). Brush/pour the melted butter across the top of the cake. Sprinkle the cinnamon sugar across the butter.Bake for another 5 minutes.If it's getting too dark, cover with aluminum foil. Remove from the oven to cool. After 5 minutes loosen the springform pan.
Serve with Whipped Cream