Pieurines in Mustard Sauce

These round sausage patties come from a village on the Normandy coast. Anywhere else in France they would be called crepinettes because the forcemeat is wrapped in caul fat (called crépine in French), which makes their outside look enticingly appetizing. Pieurine is the ancient French name which has fallen more and more in desuetude in France, but is still current in the lower valley of the St. Lawrence where the pieurine is served with a white onion sauce; the N