Brush the broiler pan with oil.
Mix 1 teaspoon of mustard and 1/2 teaspoon of paprika into softened butter. Divide basting butter to top each piece of salmon. Then, place skin side down on the broiler.
Broil for about 5 minutes. Then turn over, gently peel away the skin with a spatula and discard. Broil salmon for an additional 4-5 minutes.
Meanwhile, combine onions, basil, wine, and cream in a saucepan. Bring to a boil, stirring and reduce about 3 minutes. (Reduction is the method of boiling and evaporating the liquid for a more concentrated flavor and thicker consistency.) Then turn heat to low and add the remaining stick of butter. Stir while the sauce thickens. Finally, stir in 2 tablespoons of mustard and a dash of pepper.
Spoon sauce over each piece of salmon.