Start off by lining the cake tin with a parchment paper at the bottom and grease the sides with butter. In a bowl combine an egg, sugar, butter, flour and baking powder.
Using your hands mix all the ingredients together to form a firm dough. Crumble the pastry into the prepared cake tin. Using your hands, press the cake base until the bottom of the cake tin is covered. Make the dough a bit high on the sides as well and set aside. Preheat the oven to 175 ° C (347°F), with both top and bottom heat.
Separate the eggs into two separate bowls. Put the bowl with egg whites in the fridge. Add sugar, cream cheese, sour cream, corn flour (cornstarch), milk to the bowl with egg yolks. Whisk to a smooth cream. Add melted butter, lemon zest and freshly squeezed lemon juice and combine well. Pour ¾ of the filling into the cake base. Put aside the remaining filling for later. Bake for 45 minutes.
In the meanwhile prepare the creamy topping. Take the egg whites out of the fridge; add a pinch of salt and 2 tablespoons of sugar. Using hand mixer, whip until light and fluffy. Fold in the cream that you previously kept aside.
After 45 minutes take the cake out of the oven, spread the creamy topping over it and bake for another 20 minutes. After 20 minutes, remove from the oven and let cool completely.