'Everyberry' crumble cake with custard foam

Why everyberry? Because it is possible to add many different fruit - strawberries, raspberries, blueberries... or event currants :) It is possible to make it from one kind of fruits or to mix some of them. It is absolutely a wonderful cake. During this year's summer holidays I made it a couple of times! I do recommend preparing it with double foam (I will write below how to bake it, because it differs from the basic version).
A must-do!

Recipe from: http://www.mojewypieki.com/przepis/kruche-ciasto-z-malinami-i-lekka-budyniowa-pianka

Ingredients for the dough:

• 2,5 glasses of flour
• 250 g of cold butter or margarine 
• 2 teaspoons of baking powder
• 3 tablespoons of powdered sugar
• 5 egg yolks (do not throw away the whites, they are necessary to make the foam! Put them aside.)

Ingredients for the foam:*

• 5 egg whites
• 1 glass of sugar
• 1 packaging of vanilla sugar (16g)
• 2 packagings (40 g each) of powdered vanilla/cream custard (budyń, budyń again!) 
• 1/2 glass of oil

* I do recommend making double foam - if so, just double every ingredient - 10 egg whites (but the bottom of the cake, the dough, takes only 5 yolks, it doesn't change!) 2 glasses of sugar, etc. Then, we bake the bottom as the basic recipe says, but the second baking will take around 30-40 minutes in 170-180C.

Additional ingredients - the top:

• 500-600 g of fruit (for example 200 g of raspberries, 200 g of blueberries, 200 g of currants)
• powdered sugar, to sprinkle the top

Preparation:

1. Take a big bowl. Put the flour, baking powder, powdered sugar and egg yolks inside. Chop the butter and add it to that bowl as well. Knead it quickly. Divide the dough into 2 spheres - one 60% of the dough and another 40%. Twist every piece around a cling film and put inside the freezer for an hour or 2. (It is possible to prepare the dough one day earlier).
2. Take a rectangular pan. Grease it and put baking paper all over the pan. 
3. Take the bigger sphere from the freezer and grate it on the entire bottom of the pan(the smaller one remains in the freezer). Bake it in 190C for around 20minutes (till it gets a light-gold colour). Cool down.
4. While the cake is cooling down, wash all the fruit and put them on paper towels, to let them dry.
5. When the bottom of the cake is cooled down, start preparing the foam.
6. Take a big bowl, put egg whites inside. Beat till stiff (around 7-9 minutes). One tablespoon after another, add sugar and vanilla sugar, still mixing. Without stopping the mixer, add powdered custard and slowly, the oil.
7. Put the foam on a cooled down bottom of the cake. 
8. Put all the fruit on the foam.
9. Take the second sphere and grate it on the top of the cake.
10. Bake in 190C for 30-40 minutes.
11. Cool down, sprinkle with powdered sugar.
12. Bon, bon Appetit! :)