Royal Vatrushka

Freeze the butter for 30 minutes, then grate it.

Mix the dry ingredients, add the grated butter, and rub together. Stir in the egg and rub into crumbs (the mixture will initially clump like dough, but will then turn crumbly); add a tiny bit more flour if needed.

For the filling, combine all ingredients and blend until completely smooth.

Place 1/3 of the crumbs into a baking dish and press down firmly (this is just for the bottom layer). Pour 1/2 of the filling over it, then layer again with crumbs, filling, and top with the remaining crumbs.

Bake at 180°C (350°F) for 40 minutes, covering the pie with foil since the top browns quickly.