Preheat the oven to 375 F (200C). Peel and remove the core of the apples, and cut into thin slices. Toss with lemon juice and set aside.
In a large bowl add the eggs and sugar, and beat well with an electric mixer until light and fluffy. Add the ricotta, vanilla extract, and zest of the lemon. Beat well.
Add the almond flour, cornstarch, and baking powder. Mix until combined. Fold in about ⅔ of the apples. Save the rest for the top.
Grease or line with parchment paper a 9-inch baking pan. Add the batter and level. Top with the remaining apple slices. Bake at 375F for about 55-60 minutes, or until set in the middle. Let the cake cool down. Remove from the pan and sprinkle with powdered sugar if you like.
