Toss the mushrooms with the lemon juice. In a skillet, melt 1 tablespoon of the butter. Add the mushrooms, season with salt and pepper and cook over moderately high heat until they start to brown, about 2 minutes. Reduce the heat to moderate and cook until the mushrooms are deeply browned, about 6 minutes. Transfer to a large plate.
Add 1 tablespoon of the butter to the skillet and melt over high heat. Add the scallops to the pan in an even layer and season with salt and pepper. Cook the scallops undisturbed until they start to brown and some juices are exuded, about 2 minutes. Stir briefly, then transfer the scallops and any accumulated juices to a bowl.
Add the remaining 1/2 tablespoon of butter and the scallions to the skillet. Cook over moderately low heat, stirring, for 1 minute. Add the whiskey and carefully ignite it with a long match. When the flames die down, add the cream, mushrooms and any juices from the scallops. Simmer the sauce until slightly reduced. Add the scallops to the sauce, season with salt and pepper and serve.