Heat a large skillet over medium-high heat. Dry the lamb chops well and season with salt and pepper, to taste. Add the oil to the pan and heat until shimmering. Lay chops in the pan and cook, turning once, until an instant-read thermometer inserted into the sides of the lamb registers 125 degrees F, about 4 minutes per side. After cooking the lamb on each side, stand it up on it's edges to brown the sides as well, about 2 minutes more. Reduce the heat if needed so the browned bits remaining in the pan don't burn. Remove chops from the skillet and set aside in a warm place.
Pour off all but 1 1/2 tablespoons fat from the skillet. Add the garlic and cook, tilting the skillet to keep the garlic submerged in the fat, and cook until golden, about 1 minute. Add the wine and rosemary, stirring up browned bits from the bottom of the pan, and simmer over high heat until syrupy, about 3 to 4 minutes. Add the chicken broth and cook until reduced by about half, another 5 to 6 minutes. Remove pan from the heat and briskly whisk in the butter. When the butter has incorporated, whisk in the mustard and heavy cream. Season with additional salt and pepper.
Serve 2 chops per person with the sauce.
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