Rinse mushrooms quickly and dry well. Slice thinly. Saute onions and garlic in butter and olive oil. Add mushrooms and cook until they no longer exude water. Add sherry and cook for 5 minutes. Sprinkle with flour and stir in, tne add the stock and herbs and bake in 425 degree oven for 10 minutes. Sprinkle with chopped parsley and serve.