Ingredients
Equipment
Method
Prep the Butter and Au Jus Pan
- In a food processor, combine the softened butter, minced garlic, rosemary, thyme, and a pinch of steak seasoning. Blend until smooth to create the garlic herb compound butter.
- Season the prime rib on all sides with steak seasoning (about 1 teaspoon per pound), then generously coat the entire roast with the compound butter. Place on a raised rack.
- Fill a foil pan with the shaved red onions, beef broth, garlic clove, rosemary sprig, thyme sprig, and Worcestershire sauce. This pan catches all the drippings during the cook.
Smoke the Prime Rib
- Preheat the smoker to 275°F with applewood. Place the foil pan on the grate and position the prime rib directly above it. Smoke until the internal temperature reaches 125°F, about 2 to 3 hours depending on the size of the roast.
- Remove the roast and rest for 15 to 20 minutes. Carryover cooking brings the internal temperature to roughly 130°F for medium-rare.
Sauces and Slicing
- Strain the liquid from the foil pan through a fine mesh strainer. Reserve the au jus for dipping and set the caramelized onions aside for the sandwich build.
- In a bowl, combine the mayonnaise, grated garlic, lemon juice, horseradish, and parsley. Mix until smooth and refrigerate until ready to use.
- Using a meat slicer, shave the rested prime rib into very thin slices. Without a slicer, chill the roast 20 to 30 minutes first, then slice as thin as possible with a long, sharp knife using smooth full-length strokes.
Build and Serve
- Toast the ciabatta buns until golden and crispy. Spread garlic horseradish aioli on each bottom bun, pile on the shaved prime rib, and top with the caramelized red onions from the drip pan.
- Add 2 slices of provolone per sandwich and broil for 1 to 2 minutes until the cheese is melted, bubbly, and lightly browned. Spread more aioli on the top bun, close the sandwich, and serve immediately with warm au jus for dipping.
Notes
Smoke Directly Over the Au Jus Pan: This is the signature move. Every drop of rendered beef fat and melting herb butter falls into the broth during the 2 to 3 hour cook, building an au jus with smoke flavor and richness that no stovetop version can match. Position the roast directly above the pan, not beside it.
Pull at 125°F, Not 130°F: Carryover cooking raises the internal temperature roughly 5 degrees during the 15 to 20 minute rest, landing at 130°F for true medium-rare. Pulling at 130°F overshoots into medium territory by the time the rest finishes.
The Onions Pull Double Duty: After straining the au jus, the softened red onions from the pan go directly onto the sandwiches as the caramelized onion layer. Nothing gets wasted. Shave them thin on a mandolin so they break down fully during the cook.
Chill Before Hand-Slicing: A meat slicer produces the most consistent shaved-thin slices, but if slicing by hand, chill the rested roast in the refrigerator for 20 to 30 minutes first. Slightly firm beef shaves cleanly while warm beef tears.
Fresh Herbs Only in the Butter: Fresh rosemary and thyme release aromatic oils gradually as the butter melts. Dried herbs burn and turn bitter under prolonged smoker heat. Don't substitute.
Don't Skip the Broiler Step: Laying cold provolone on warm meat leaves it semi-melted. The 1 to 2 minute broil transforms the cheese into a molten layer that fuses the beef and onions together. Watch closely — the line between bubbly and burnt is about 30 seconds.
Leftover Prime Rib Version: Using holiday leftovers? Skip the smoke. Simmer the au jus ingredients in a saucepan for 20 to 25 minutes and strain. Slice the cold prime rib thin, dip slices in the warm au jus for 30 to 60 seconds to gently reheat, and build as directed. Done in under 45 minutes.