In a 10 - 12" skillet combine 3 tablespoons butter and the oil and saute the onion and celery over low heat for 4- 6 minutes or until soft. Add the flour, a little at a time and cook stirring for 3 - 4 minutes. Meanwhile, heat milk and cream in a small saucepan. Add the heated milk gradually to the onion mixture, stirring constantly.
In a small bowl combine the dry mustard, Tabasco, Worcestershire, sherry, lemon juice, and parsley. Add this mixture to the onion mixture in the skillet, stirring well. Bring to a simmer and stir until the sauce thickens, about 3 - 4 minutes. Add the chopped eggs and crab. Taste for seasoning, adding salt and pepper to taste.
Divide the mixture between 6 scallop shells or ramekins. Dot them with the remaining butter and cover with the cheese. Place them in a pre-heated 375 F oven for 15 minutes or until they are lightly browned and bubbling. Serve as a first course. Note: This can also be served as a main course by placing the crab mixture in a shallow casserole and accompanying it with Sourdough Bread and a fresh spinach salad!