Jus des Rognons, or, Kidney Gravy

• Mutton kidneys, 3
• butter, 2 oz.
• onion, 1

Strip the skin and take the fat from three fresh mutton kidneys, slice and flour them; melt two ounces of butter in a deep saucepan, and put in the kidneys, with an onion cut small, and a teaspoonful o