Salt the roast ahead
Pat the roast dry. Rub the meat evenly with the kosher salt (about 30 g, roughly 1% of the roast weight). Cover and refrigerate for at least 24 hours — this dry-salt rest seasons deeply and improves the final crust.

Bring to room temperature & preheat
On the day you’ll cook, take the roast out of the fridge and let it come toward room temperature (the original timing suggests several hours; aim to remove it well in advance so it’s not stone cold going into the oven). Preheat your oven to 250°F (120°C) and position a low rack to fit the roast.

Trim & tie if needed
If your butcher removed the rib bones, reattach or tie them back on so the roast cooks evenly and is easier to carve later.

Brown bones and build flavor for the jus
Heat the olive oil in a large stockpot over medium heat. Add the beef bones and brown thoroughly on all sides — this can take 10–12 minutes and develops deep flavor. Add the smashed garlic, chopped carrots, celery and the quartered onion; cook until the vegetables soften. Stir in the tomato paste and cook a few more minutes to caramelize.

Deglaze and simmer the broth
Pour in the red wine to deglaze the pan, scraping up any browned bits from the bottom. Add the beef stock, thyme sprigs and bay leaf. Bring to a boil, then lower to a gentle simmer and let it cook while the roast is in the oven so the liquid reduces and concentrates into a rich au jus.

Roast low and slow
Insert a probe thermometer into the thickest portion of the roast (avoid touching bone). Place the roast, fat-side up, on a rack in a roasting pan and slide it into the 250°F oven. Roast until the internal temperature reaches about 115°F for rare or 120°F for medium-rare — this usually takes roughly 3 hours for a 6-lb roast, but times will vary by oven and roast size. Rely on the thermometer, not the clock.

Rest the meat
Remove the roast from the oven and loosely tent it with foil. Let it rest for 20–30 minutes so the juices redistribute and the carryover heat brings the roast a few degrees higher.

Make the horseradish sauce
While the roast rests, whisk together the sour cream, prepared horseradish, Dijon mustard, Worcestershire sauce and mayonnaise in a bowl until smooth. Adjust seasoning to taste and chill until serving.

Finish the roast for a crust
After the rest, place the roast under the broiler (or increase oven heat to high) and brown the exterior for 1–2 minutes per side to develop a caramelized crust — watch it closely so it doesn’t burn. Remove and let the roast sit a couple minutes before slicing.

Strain and finish the au jus
Strain the simmered broth through a sieve, discarding solids. Skim excess fat from the top (paper towels or chilled fat removal can help). Adjust seasoning with salt and pepper. Keep the jus warm for service.

Carve and serve
Slice the roast against the grain into even pieces. Serve immediately with warm au jus and a dollop of horseradish cream on the side.