I love this dish. So creamy and delicious. I can't remember where I got this recipe from. It is the one I turn to all the time. I have the ceramic scallop shells for this dish. You can also add a dash of cayenne pepper to the sauce
Combine the ingredients for the bouillon with only 1/2 cup of wine in a medium saucepan. Bring to a boil and simmer 10 minutes. Add other 1/2 cup wine and scallops and simmer another 5 minutes. Drain and reserve liquid and scallops only.
Melt butter and saute onions and mushrooms until tender. Remove from heat and stir in flour and pepper, blend well. Put back on heat and gradually stir in cream, bring just to boiling stirring constantly. Reduce heat and simmer until thick 4-5 minutes. Add Gruyere and stir until melted. Remove from heat , stir in wine and 1/2 cup prepared bouillon and parsley. Add scallops and mix well. Divide into 6 scallop shell dishes.
Peel potatoes and dice and cook. Mash potatoes with butter,milk,salt, pepper and yolk. Pipe potatoes around scallop shells on the edges only using pastry bag and star tip. Sprinkle with Parmesan cheese all over.
Place shells on baking sheet or cookie sheet. Broil 4 " from heat on low until golden brown and heated through. About 2-3 minutes. Depends how cool things became when assembling you can also put in 400F oven for a few minutes first then on broil.