In baking dish rub 1 tablespoon butter on the bottom and sprinkle some chopped shallots all over. Arrange the bass on top and sprinkle some salt and pepper. Dot with 1 tablespoon butter. Add the champagne and cover with a wax paper. Bake in a 450 degree oven for 10 minutes. Lift up the bass and place them on a large platter.
In a skillet melt one tablespoon butter and add the flour. Let cook for a few seconds. Add the liquid from the baking dish and whisk together. Add the cream and mustard. Let reduce until the right consistency. Adjust seasoning and add the lemon juice. Pour the sauce over the cooked sea bass and serve immediately.
