A specialty at Fore Street restaurant in Portland, Maine.
Preheat oven to 400°. Prepare mussels; discard any that are broken, slack, or too heavy (filled with mud). Remove beards and scrape barnacles and limpets. Rinse well and set aside.
On a baking sheet, roast almonds 4–5 minutes or until fragrant. Cool, and chop by hand (or pulse in a food processor) to consistency of coarse meal. Set aside.
In an ovenproof metal gratin dish or skillet (large enough to hold mussels in one or two layers, no more) over medium heat, melt 1 tablespoon butter. Add shallot and garlic and cook 2–3 minutes. Add cider and lemon juice, and bring to a boil. Remove from heat. Add herbs, almonds, salt, and pepper.
Raise oven temperature to 450°. Arrange mussels in one or two layers over cider/almond mixture. Cut remaining butter into half-inch pieces and distribute over mussels. Roast 3–4 minutes. Stir to baste. Repeat until mussels have opened and butter sauce is creamy and fragrant (don’t overcook). Serve directly from pan with coarse-textured, crusty bread.