2) After cooking the lamb on each side, stand it up on its edges to brown the sides as well, about two minutes more. Reduce the heat if needed so the browned bits remaining in the pan don't burn. Remove the chops from the frying-pan and set aside in a warm place.
3) Pour off all but 1 1/2 tablespoons of fat from the frying-pan. Add the garlic, tilting the pan to keep the garlic submerged in the fat, and cook until golden, about one minute. Add the wine and rosemary, stirring up the browned bits from the bottom of the pan, and simmer over a high heat until syrupy, about three to four minutes.
4) Add the chicken stock and cook until reduced by about half, another five to six minutes. Remove the pan from the heat and briskly whisk in the butter. When the butter has been incorporated, whisk in the mustard and double cream.
5) Season with additional salt and pepper, to taste. Serve two chops per person with the sauce.