Saute minced onion in 1/4 cup butter.Add lemon juice.Place escargot in mushroom caps in individual dishes.Spoon onion and butter over escargot.Sprinkle lightly with garlic powder.Let stand for two hours. Pour mixture of remaining butter and garlic powder over escargot.Bake @ 350 degrees for 10 to 15 minutes.Serve with garlic toast. * To Blanch Escargot: Blanching is the first step in preparing escargot dishes.Fill a 3 quart pan half full of water (enough to cover the snails).When water boils,drop in the rinsed snails.Boil vigorously for 3 minutes (no more or the snails will get tough).Remove snails and rinse in cold water.Remove nails from shells with a toothpick.Place snails in bowl containing a mixture of half water and half vinegar for two hours.Snails are now ready to simmer in sauces.They may be cut into two or three pieces,if desired.Blanched snails,may be frozen.Note: Do not save snail shells,which are fragile.