While beef is resting, pour roast juices into a skillet set over medium-high heat. Add butter and stir until melted. Add broth, thyme and mustard and bring to a boil. Boil, whisking often, until sauce is reduced by half and slightly thickened, about 10 min. Whisk in cream and pepper.
Tip: This simple yet addictively good gravy upgrade is a must-make this holiday.