Trim the escalopes and, using the flat side of a a meat mallet or a rolling pin, beat or roll them out thinly between sheets of plastic wrap. Coat the pieces with the seasoned flour.
Heat the butter in a large frying pan and brown the escalopes well on both sides, two at a time, if necessary. Add the grated lemon rind, mace and white wine and simmer, uncovered, for about 5 minutes, or until the meat is tender. Transfer the escalopes from the frying pan to a heated serving dish, cover and keep the dish warm.
Boil the sauce until slightly reduced. Mix the egg yolk with the cream and stir into the sauce. Reheat the sauce without allowing it to boil. Season to taste and strain through a small sieve over the escalopes. Garnish with the parsley sprigs and the lemon wedges.