Place fish in a baking dish - ensure the fish isn't crammed in too snugly. See video or photos in post. Sprinkle both sides of fish with salt and pepper.
Place butter, cream, garlic, mustard, lemon juice, salt and pepper in a microwave proof jug or bowl. Microwave in 2 x 30 sec bursts, stirring in between, until melted and smooth.
Sprinkle fish with shallots, then pour over sauce.
Bake for 10 - 12 minutes, or until fish is just cooked. Remove from oven and transfer fish to serving plates. Spoon over sauce, and garnish with parsley and lemon wedges if using.