in a small pot, heat oil over medium. Add shallots, season with salt, pepper, and cayenne (if using) and cook, stirring, until tender, 4 minutes. Add broth, cream and lemon zest. Bring to a boil and cook until slightly thickened, 8 minutes. Add lemon juice, basil leaves and season to taste with salt and pepper. Spoon sauce over fish. Makes enough sauce for 4 servings of grilled or broiled or baked fish.