Heat up 2/3 of milk quantity with sugar till sugar melts fully. Put together an egg (55gr.), flour and 1/3 quantity of milk and stir until smooth. Very accurately pour the egg mix into slightly heated milk with sugar, stir intensively. Cook till the mixture thickens (up to 85⁰C), do not stop stirring. Tightly cover the mixture with plastic film and cool to reach room temperature, whip butter until white, continue whipping and add the mixture in three portions.

Use one crust to make the crumb topping.