Melt butter in a pan, chop shallots and sauté until light. Deglaze with Noilly-Prat and white wine and boil down until almost all the liquid has evaporated. Add fish stock and reduce again to half to one third. Add whipped cream and cook for another 5 minutes. Season to taste with salt, pepper, cayenne pepper and lemon juice. Strain through a fine kitchen towel.