Apple Custard Cake

In a large bowl, beat the eggs, sugar, oil, butter and lemon zest until well combined.
Add flour and baking powder, mix until fully incorporated. You will need to combine the dough with your hands until smooth. Separate ¼ of the dough, wrap in a plastic a wrap and refrigerate for 30 minutes for later use.
Grease a 9x9 inch springform pan with oil or butter. Spread the remaining dough on the bottom of the spring form pan, smooth the top with the hands. Place the springform pan in the refrigerator for few minutes.
Peel and dice one big apple and put it in a saucepan along with lemon juice and sugar. cook for 5 minutes or until the apple has softened a little bit. Remove from the heat.
In another sauce pan, add milk, egg yolk, sugar, vanilla extract and corn flour. Whisk until combined, then cook for 5 minutes on low heat until thickened. Add whipping cream and cook for few more minutes. Remove from the heat.
Add softened apple to the custard mixture. Now pour the custard mixture on the prepared pan. Grate the ¼ reserved dough on top.
Bake at preheated 355F (180C) oven for 25 minutes. Let the cake cool completely before cutting and serving.