- 1/4 cup coarse fresh bread crumbs from a baguette
- 1/4 cup finely grated Parmigiano-Reggiano
- 1 1/4 cups dry white wine
- 1 cup water
- 1/2 small onion, sliced
- 1/4 bay leaf
- 1/2 teaspoon salt
- 1/4 teaspoon black pepper
- 1 pound sea scallops, tough muscle removed from side of each if necessary and scallops cut into 3/4-inch pieces
- 1/2 pound small mushrooms, halved lengthwise, then thinly sliced lengthwise
- 6 tablespoons unsalted butter
- 1/2 cup heavy cream
- 1 large egg yolk
- 1 tablespoon all-purpose flour
- 8 cups kosher salt to stabilize scallop shells (if using)
- 1 1/2 tablespoons minced fresh flat-leaf parsley
- Special equipment: 16 (2 1/2-inch) scallop shells or 8 (2-oz) ramekins
- Preheat oven to 350 degrees F.
- Toast bread crumbs on a baking sheet in middle of oven until pale golden, 6 to 8 minutes, then toss with cheese.
- Simmer wine, water, onion, bay leaf, salt, and pepper in a 2 1/2- to 3-quart heavy saucepan, uncovered, 5 minutes, then add scallops and simmer, uncovered, stirring occasionally, until just cooked through, 2 to 3 minutes. Transfer scallops to a platter with a slotted spoon to cool, returning any onions to pan, then boil cooking liquid until reduced to about 1 cup, 8 to 10 minutes. Pour cooking liquid through a sieve into a bowl.
- Cook mushrooms in 2 tablespoons butter in a 10- to 12-inch heavy skillet over moderate heat, stirring occasionally, until most of liquid mushrooms give off is evaporated, about 5 minutes. Season with salt and pepper.
- Whisk together cream and yolk in a heatproof bowl. Melt 2 tablespoons butter in cleaned 2 1/2- to 3-quart saucepan over moderately low heat, then add flour and cook roux, whisking, 2 minutes. Remove pan from heat and add reduced cooking liquid in a stream, whisking constantly. Return pan to heat and simmer, whisking, 1 minute. Pour sauce in a slow stream into cream mixture, whisking constantly, then pour sauce back into pan and simmer, whisking, 1 minute. Remove from heat and season with salt and pepper.
- Preheat broiler.
- Stir scallops and mushrooms into sauce, then divide among scallop shells or ramekins and sprinkle with bread crumb mixture. If using shells, spread kosher salt evenly in a large shallow baking pan, then nestle shells in salt. Dot scallops with remaining 2 tablespoons butter, then broil about 4 inches from heat until golden, about 2 minutes. Sprinkle with parsley.