Quick Recipe Version (TL;DR)
Quick Ingredients
- 3 lb boneless prime rib (ribeye roast)
- 1 1/2 tsp kosher salt, 1 1/2 tsp black pepper, 1 tsp garlic powder, 1 tsp smoked paprika, 1 tsp light brown sugar (optional), 1 tbsp neutral oil
- 2 large yellow onions, 2 tbsp unsalted butter, 1 tbsp olive oil, 1/2 tsp kosher salt, 1 tsp thyme leaves, 1 tbsp balsamic vinegar
- 1/2 cup mayonnaise, 2 tbsp prepared horseradish (drained), 1 tsp Dijon mustard, 1 tsp lemon juice, 1/4 tsp kosher salt, 1/8 tsp black pepper
- 12 mini brioche or potato rolls, 1 tbsp melted butter (for toasting)
- Optional: 2 cups baby arugula
Do This
- 1) Caramelize onions over medium-low heat 40–50 minutes; finish with balsamic.
- 2) Stir together horseradish mayo; chill.
- 3) Heat smoker to 225°F and preheat a cast-iron skillet or grill for searing later.
- 4) Season prime rib; smoke at 225°F to 118°F internal (about 2–3 hours).
- 5) Sear over very high heat to deepen crust; pull at 125°F for medium-rare.
- 6) Rest 20 minutes; slice paper-thin across the grain.
- 7) Toast rolls, spread horseradish mayo, add onions + prime rib (and arugula if using); serve warm.
Why You’ll Love This Recipe
- It tastes like a steakhouse sandwich, but in a crowd-friendly slider you can eat one-handed.
- Reverse-sear smoking gives you a rosy, juicy center with a crisp, flavorful crust.
- Horseradish mayo + caramelized onions bring creamy heat and deep sweetness to balance the rich beef.
- Easy to scale up for parties, game days, and “fancy BBQ” gatherings.
Grocery List
- Produce: 2 large yellow onions, 1 lemon, fresh thyme (or dried), optional baby arugula
- Dairy: unsalted butter
- Meat: 3 lb boneless prime rib (ribeye roast)
- Bakery: 12 mini brioche or potato rolls
- Pantry: mayonnaise, prepared horseradish, Dijon mustard, balsamic vinegar, olive oil, neutral oil, kosher salt, black pepper, garlic powder, smoked paprika, light brown sugar (optional)
Full Ingredients
Prime Rib
- 1 (3 lb) boneless prime rib (ribeye roast), tied (ask the butcher to tie it, or tie with kitchen twine)
- 1 1/2 tsp kosher salt
- 1 1/2 tsp freshly ground black pepper
- 1 tsp garlic powder
- 1 tsp smoked paprika
- 1 tsp light brown sugar (optional, helps browning)
- 1 tbsp neutral oil (avocado, grapeseed, or canola)
- Wood suggestion: oak or hickory (or a 50/50 blend)
Caramelized Onions
- 2 large yellow onions, thinly sliced (about 1 1/2 lb / 680 g)
- 2 tbsp unsalted butter
- 1 tbsp olive oil
- 1/2 tsp kosher salt, plus more to taste
- 1 tsp fresh thyme leaves (or 1/2 tsp dried thyme)
- 1 tbsp balsamic vinegar
- 2 tbsp water (as needed, to deglaze if the pan gets too dry)
Horseradish Mayo
- 1/2 cup mayonnaise
- 2 tbsp prepared horseradish, drained
- 1 tsp Dijon mustard
- 1 tsp fresh lemon juice
- 1/4 tsp kosher salt
- 1/8 tsp black pepper
For Serving
- 12 mini brioche rolls or mini potato rolls, split
- 1 tbsp melted butter (for toasting rolls)
- 2 cups baby arugula (optional, for a peppery fresh crunch)
Step-by-Step Instructions
Step 1: Caramelize the onions low and slow
Heat a large skillet over medium-low heat. Add the 2 tbsp butter and 1 tbsp olive oil. When the butter is melted, add the sliced onions and 1/2 tsp kosher salt.
Cook, stirring every few minutes, until the onions are deeply golden and jammy, 40–50 minutes. If the pan starts to look dry or you see browned bits getting too dark, splash in 1–2 tbsp water and scrape up the fond.
Stir in the thyme and 1 tbsp balsamic vinegar. Cook 1–2 minutes more, then remove from heat. Keep warm, or cool and refrigerate (see storage notes below).
Step 2: Make the horseradish mayo
In a small bowl, mix together 1/2 cup mayonnaise, 2 tbsp prepared horseradish, 1 tsp Dijon, 1 tsp lemon juice, 1/4 tsp kosher salt, and 1/8 tsp black pepper.
Cover and refrigerate until serving time. (It tastes even better after 15–30 minutes in the fridge.)
Step 3: Preheat the smoker and plan your sear station
Preheat your smoker to 225°F. Add your wood (oak or hickory are great here).
Also set up your searing method for later: either preheat a grill to 500°F, or plan to heat a large cast-iron skillet over high heat near the end of the smoke.
Have an instant-read thermometer ready; temperature control is what makes prime rib sliders feel “fancy” without extra work.
Step 4: Season the prime rib
Pat the roast dry with paper towels. Rub all over with 1 tbsp neutral oil.
In a small bowl, combine 1 1/2 tsp kosher salt, 1 1/2 tsp black pepper, 1 tsp garlic powder, 1 tsp smoked paprika, and 1 tsp brown sugar (if using). Coat the roast evenly on all sides, pressing the seasoning in so it adheres.
Tip: If you have time, season the roast and refrigerate uncovered for 8–24 hours for deeper flavor. If not, cook right away.
Step 5: Smoke until medium-rare (reverse sear)
Place the prime rib on the smoker grates. Smoke at 225°F until the internal temperature in the thickest part reaches 118°F, about 2–3 hours for a 3 lb roast (time varies by smoker and roast shape).
Keep the lid closed as much as possible and use temperature, not the clock, to guide you.
Doneness note: Pulling at 118°F sets you up to finish around medium-rare after the sear and rest. If you prefer medium, you can smoke to 123°F and then sear briefly.
Step 6: Sear for a steakhouse crust, then rest
Sear immediately after smoking.
Skillet method: Heat a cast-iron skillet over high until very hot. Add the roast and sear 60–90 seconds per side, including edges, until browned and crisp.
Grill method: Place the roast over direct heat at 500°F and sear 1–2 minutes per side.
Pull the roast when the internal temperature reaches 125°F for medium-rare. Rest on a cutting board, loosely tented with foil, for 20 minutes. The temperature should rise to about 128–132°F during the rest.
Step 7: Slice thin and build the sliders
While the roast rests, brush the cut sides of the rolls with 1 tbsp melted butter and toast on a skillet or grill over medium heat until lightly golden, 1–2 minutes.
Slice the prime rib as thinly as you can across the grain. (If you want ultra-thin deli-style slices, chill the cooked roast for 30–45 minutes first to firm it up, then slice.)
Assemble each slider: spread 1–2 tsp horseradish mayo on the bottom bun, add a small pinch of arugula (optional), pile on a few folds of prime rib, and top with a spoonful of caramelized onions. Cap with the top bun and serve warm.
Pro Tips
- Use a thermometer, not guesswork: Prime rib goes from perfect to overcooked quickly. Target 118°F before searing and 125°F after searing for medium-rare.
- Thin slices make the slider: Even if your roast is thick, shaving it thin makes every bite tender and “steakhouse sandwich” worthy.
- Don’t rush the onions: Keep heat at medium-low and give them the full 40–50 minutes for deep sweetness.
- Toast the buns: It helps the sliders hold up to the mayo and juicy beef without getting soggy.
- Season at the end if needed: A tiny pinch of flaky salt on the sliced beef right before serving can make flavors pop.
Variations
- Au jus dip sliders: Warm 1 cup beef broth with any resting juices from the cutting board, plus a pinch of salt and pepper. Serve alongside for dipping.
- Spicy horseradish mayo: Add 1 tsp hot sauce or 1/2 tsp cayenne to the mayo for extra heat.
- Cheesy steakhouse sliders: Add 12 thin slices provolone to the toasted buns and melt briefly before adding beef and onions.
Storage & Make-Ahead
Make ahead: Caramelized onions can be made up to 4 days ahead and refrigerated. Horseradish mayo can be made up to 3 days ahead. You can smoke and sear the prime rib up to 1 day ahead, cool, wrap tightly, and refrigerate; slice thin cold, then gently warm the slices (covered) in a 300°F oven for 8–10 minutes or just serve at room temperature for easy party service.
Store: Keep beef, onions, mayo, and rolls separate in airtight containers. Refrigerate beef for up to 3 days. Refrigerate onions for up to 4 days. Refrigerate horseradish mayo for up to 3 days.
Reheat: Warm sliced beef gently (avoid high heat or it will overcook). Reheat onions in a skillet over low heat with a splash of water.
Nutrition (per serving)
Approximate, per serving (2 sliders): 690 calories, 34 g protein, 45 g fat, 34 g carbohydrates, 2 g fiber, 7 g sugar, 760 mg sodium.
