Cook the chopped onion in a wide pan until golden then add 400 grams smoked pancetta/bacon, add salt and pepper and cook on a low flame. Add the 500 grams rice and toast slightly maintaining a medium flame, add 1 litre stock and when boiling lower the flame and continue cooking for 15 minutes. When the rice has absorbed the broth, turn off and add 300 g Fontina cheese and mix in well. In the meantime take the roll of puff pastry, place it on a pastry board, and roll it out until it is the size of a 35 cm mould, then take a round 20 cm quiche dish and place the pastry in it. Pour the mixture into the pastry case, then take the sides and cover the mixture pressing slightly and brush the surface with the egg yolk. Cook in an oven at 200 degrees for 20 minutes.
For the sauce
Bring 500 ml milk to the boil in a saucepan with a pinch of salt. In another saucepan place the butter and cook until golden continuing to stir, then add the flour and the milk. When the sauce has thickened slightly, add the Stracchino cheese and mix adding also the chopped parsley (if the sauce is too thick add a little meat stock). Serve in wedges and sprinkle with the stracchino sauce.