Loin of Lamb Stewed in Butter (Entrée)

Wash the joint, and wipe it very dry; skewer down the flap, and lay it into a close-shutting and thick stewpan or saucepan, in which three ounces of good butter have been just dissolved, but not allowed to boil; let it simmer slowly over a very gentle fire for two hours and a quarter, and turn it when it is rather more than half done