Rinse mushrooms clean and remove stems. Discard stems or save for another purpose. Combine butter, garlic, shallots and parsley in the work-bowl of a food processor or small bowl. Process or mix until combined. Add lemon juice, salt and pepper. Blend briefly. Place mushrooms in a shallow baking dish. Fill each mushroom cap with a dollop of the garlic butter mixture (about ½ to 1 tsp). Bake at 400ºF for 10 - 12 minutes or until bubbly. Serve with crusty French bread if desired. Use toothpicks to spear the mushrooms. Urge guests to dip bread into the remaining butter. Provide small plates and plenty of napkins.