Preheat oven to 400˚F.
In a small bowl, stir together coffee grounds, minced thyme, minced rosemary, chipotle chili powder, pepper, and kosher salt until combined.
Rub both racks evenly with the rub.
Heat oil vegetable oil in a large cast iron skillet over medium-high heat. Sear on both sides, about 1 minute per side.
Place skillet in the oven and roast until internal temperature is 145˚F. This should take about 20 to 25 minutes. Let lamb rest about 5 to 10 minutes before slicing.
While the lamb is roasting, make the red wine sauce. In a medium saucepan, heat the olive oil over medium-high heat. Once hot, add garlic and brown slightly, about 1 minutes.
Stir in cornstarch until garlic is coated. Pour in wine and beef stock, whisking to combine. Allow mixture to cook and reduce by half, about 5 to 7 minutes.
Stir in butter and rosemary. Once butter has melted, season with salt and pepper to taste. Keep warm over low heat.
Serve lamb with warm sauce.