Ingredients
Scale
The Roast
- 1 standing rib roast, 3–4 ribs, bone-in (approximately 7–10 lbs)
- 1 tbsp kosher salt per 2 lbs of roast (for dry brine)
The Herb Paste
- 4 tbsp (60g) unsalted butter, softened
- 6 cloves garlic, minced
- 2 tbsp fresh rosemary, finely chopped
- 2 tbsp fresh thyme leaves
- 1 tbsp fresh sage, finely chopped
- 1 tbsp Dijon mustard
- 1 tbsp olive oil
- 1 tsp coarsely ground black pepper
The Vegetable Rack
- 1 large onion, roughly quartered
- 2 carrots, roughly chopped
- 2 stalks celery, roughly chopped
- 1 head garlic, halved crosswise
- 2–3 sprigs fresh rosemary and thyme
- 2 bay leaves
The Liquid
- 1 cup (240ml) low-sodium beef broth
The Au Jus
- Strained drippings from the slow cooker
- 1 cup (240ml) additional beef broth
- Salt, pepper, and a squeeze of lemon
Horseradish Cream (served alongside)
- ½ cup (120g) sour cream
- 3 tbsp prepared horseradish
- 1 tbsp Dijon mustard
- 1 tsp fresh lemon juice
- Salt and pepper to taste
Instructions
- Dry brine 24–48 hours ahead. Pat the roast completely dry. Apply kosher salt generously to every surface — approximately ½ teaspoon per pound of meat. Place bone-side down on a rack set over a rimmed baking sheet. Refrigerate uncovered for 24 to 48 hours. Do not skip this step.
- Apply the herb paste. 1 hour before cooking, remove the roast from the fridge. Combine all herb paste ingredients in a small bowl. Rub the paste generously over every surface of the salted roast, pressing firmly so it adheres completely.
- Build the vegetable rack. Arrange the quartered onion, carrots, celery, halved garlic head, and fresh herb sprigs on the bottom of the slow cooker insert. Add the bay leaves. Pour the beef broth over the vegetables.
- Place the roast. Place the prime rib, bone-side down, on top of the vegetable rack. The roast should be elevated above the liquid.
- Cook on LOW. Set the slow cooker to LOW and cook until the internal temperature reaches 5°F below your target — for medium-rare (the ideal for prime rib), pull at 125–130°F (before the broiler adds the final degrees). Begin checking with an instant-read thermometer at the 4-hour mark for a 7-lb roast. A larger roast may take 6 to 8 hours. Check every 30 to 45 minutes once within 15°F of target.
- Rest while preparing the broiler. Transfer the roast to a large roasting pan or rimmed baking sheet, bone-side down. Tent loosely with foil and rest for 15 minutes while the broiler preheats and you strain the drippings.
- Strain the drippings. Pour all the liquid from the slow cooker through a fine-mesh sieve into a heatproof jug. Press the vegetables to extract maximum flavor. Skim the fat. Set aside for the au jus.
- Broil the crust. Remove the foil. Slide the roast under a preheated broiler at HIGH, 6 inches from the heat. Broil for 5 to 10 minutes, watching continuously, until the herb crust is deeply browned, sizzling, and caramelized. The internal temperature will rise 5 to 8°F during this time.
- Rest — this is mandatory. Transfer to a carving board and rest loosely tented with foil for 20 to 30 minutes. Do not carve early. The juices need this time to redistribute.
- Make the au jus. While the roast rests, pour the strained drippings into a small saucepan. Add additional beef broth to desired volume. Simmer over medium-high heat for 5 to 8 minutes until slightly reduced. Season with salt, pepper, and a small squeeze of lemon.
- Make the horseradish cream. Combine all ingredients, stir well, and taste. Refrigerate until serving.
- Carve and serve. Carve by slicing between the ribs for individual bone-in portions, or across the grain into ½ to ¾-inch slices for boneless-style serving. Serve on a warm platter with au jus in a warm jug alongside and horseradish cream in a small bowl.
Notes
- The dry brine is the most important step. Forty-eight hours is better than twenty-four. The salt penetrates the meat deeply, seasons from the inside, and dries the exterior for a dramatically better broiler crust. Make this happen.
- Medium-rare is the target. Prime rib cooked to medium-rare (130–135°F after resting) is the version that honors the quality of the cut. Above 140°F, the fat stops rendering into the meat and the texture changes from silky to firm. Pull from the slow cooker at 125–130°F — the broiler and the rest will carry it to 135°F.
- The thermometer is mandatory. Slow cooker temperatures vary between models and prime rib roasts vary in shape, bone density, and starting temperature. There is no reliable time estimate for doneness. The thermometer is the only truth.
- The rest is mandatory. A 20 to 30 minute rest for a roast of this size is not optional. The interior temperature continues to rise during resting (carry-over cooking) and the juices need time to redistribute. Cutting early produces a disappointing, dry-edged result.
- The slow cooker produces an even pink from edge to center. This is the great advantage over oven roasting. The oven produces a gradient — very well-done at the edges, perfectly pink in the center. The slow cooker’s even heat produces the same temperature throughout — every slice is equally beautiful.
- Save the vegetables and bones. The slow cooker vegetables are deeply flavored and make an excellent addition to beef soup or stew. The bones, after the meal, are extraordinary for beef bone broth.
- Prep Time: Dry Brine; 24–48 hours ahead - Prep Time20 minutes
- Cook Time: 5 – 8 hours (on LOW, depends on roast size)
- Category: Dinner, Holiday, Main Dish
- Method: Slow Cooking
- Cuisine: American, British
- Diet: Dairy-Free, Gluten-Free