Prep the sous vide water bath: Preheat the sous vide water bath to 133°F/56°C for medium-rare plus. (medium-rare is 130°F/54.5°C; medium is 138°F/59°C; and rare is 120°F/49°C).
Season and vacuum seal the roast: Measure a roll of vacuum bag long enough to fit the roast. Seal one side of the bag, then season the roast with the salt, slide it into the bag, and vacuum seal the bag.
Sous Vide the roast: Put the bagged roast in the sous vide water bath, and sous vide for 6 to 10 hours. (8 to 12 hours if the roast is frozen.) Remove the roast from the vacuum bag, saving the juices in the bag.
Start the red wine sauce: When the roast has 10 minutes left to cook, put the red wine and shallots in a small saucepan over low heat and simmer. Let the red wine simmer while you sear the roast, about 15 minutes total.
Sear the roast: Preheat a large frypan over medium-high heat until it is ripping hot. (Or, in a 425°F oven for at least 20 minutes, then put it over medium-high heat on the stovetop.) Sear the roast for 1 minute per side, starting with the fat side of the roast, until it is browned on all sides. (Treat the roast like it has 6 sides – the 4 wide sides, plus the two edges)
Finish the red wine sauce: Pour the sous vide bag juices into the simmering pot with the red wine and shallots. Taste the sauce and add salt and pepper as needed – you want the sauce to be highly seasoned.
Slice and serve: Sprinkle the roast with the fresh ground mixed peppercorns. Slice the roast into 1/2 inch thick slices and serve, passing the red wine sauce at the table.