Whip egg whites using a mixer until they are firm.
Add sugar slowly.
When egg whites and sugar are well blended add lemon juice.
Transfer the mixture onto parchment paper placed inside a baking pan.
Let the cake bake at 250 F for 1hour.
After its done let it cool for 15-20 minutes.
Place one large pot filled with water half way on the stove to boil.
Place jars of nutella into hot water so it softens while you prepare the custard
While you wait for the water to boil mix the egg yolks, eggs, flour, sugar, and 2 tablespoons of milk. Mix it in a pot that can fit inside the larger pot with boiling water. If you have a double boiler that's perfect!
When the water starts boiling reduce it to a simmer and place the pot with the mixed ingredients on top of the pot with boiling water.
Slowly add the rest of the milk.
Cook until the mixture thickens. Stir continuously to avoid burning and/or scrambled eggs!
Remove from heat and let cool.
When the custard is luke warm add previously whipped butter.
Add 3 vanilla sugars into 1/3 of the custard (white custard).
Add softened nutella into the remaining 2/3 of the custard (chocolate custard).
Whip the whipping cream.
Layer the cake.
White custard mixture.
Graham crackers briefly dipped into milk.
Chocolate custard mixture.
Optional: crush some of the graham crackers and spread the crumbs on top of the whipped topping.