Pollo Alla Valdostana

1 chicken breast, skinned, boned and butterflied
1 egg, beaten well
2 ounces Fontina cheese
2 tablespoons freshly-grated parmesan cheese
Olive oil
1 ounce butter
1/2 cup white mushrooms, thinly sliced
1/4 cup fresh green peas
2 slices prosciutto, diced
1/2 cup sherry
1 cup beef stock (may used canned)

Combine cheeses, spread down center of the butterflied breast's under-side. Fold sides of breasts under and carefully dip into beaten egg. Saute in a little olive oil and brown on both sides. Discard oil, add 1 ounce of butter to the pan, melt. Add mushrooms, mix well, add minced prosciutto and green peas, mix for 1 minute. Add sherry and beef stock. Over a low flame, cook the ingredients for 5 to 7 minutes to allow sauce to reduce. Serve hot.