Put two tablespoonfuls of butter into a saucepan. When it has melted, stir in one tablespoonful of flour that has been mixed with a little milk, and stir this over the fire until well mixed, but not browned at all; then pour in by degrees, while still stirring, one pint of milk and white stock, mixed in equal quantities, add one large carrot cut into halves, one small onion, a few sprigs of parsley, and salt and pepper to taste. Put into the sauce whatever meat is intended for the fricassee, and stew it gently by the side of the fire until tender, with the lid placed tightly on the saucepan. Strain the sauce through a silk sieve into another saucepan, thicken it with the yolks of two eggs, and squeeze in the juice of half a lemon. Serve while hot.