Preheat oven to 400 degrees F. In a large sauce pan melt butter. Whisk in flour till smooth. Gradually add cream. Bring to a boil, cook and stir for 2 min or until thickened. Add 1 cup cheese plus the salt, mustard, dill, basil and cayenne. Stir till all the cheese is melted. Remove from heat and stir in shrimp.
Place salmon in a greased baking dish. Pour shrimp mixture over salmon. Then sprinkle the other half cup of cheese over salmon.
Bake uncovered at 400 degrees for 25-30 min or till fish flakes easily with a fork and shrimp turn pink.