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Sliced two-bone prime rib tomahawk with roasted garlic and onion compound butter melting over each slice on a cutting board

Tomahawk Prime Rib with Garlic Onion Butter

A two bone prime rib tomahawk, about 6 lbs, seasoned the night before, forward seared over high heat on all sides and edges, then finished at 275°F on indirect heat to 135°F internal. Rested 20 minutes, cut between the bones into two steaks, and finished with a compound butter of roasted garlic, white onion sautéed down with soy sauce, parsley, rosemary and thyme.
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Prep Time 30 minutes
Cook Time 3 hours
Resting Time 20 minutes
Total Time 3 hours 50 minutes
Servings: 8 servings
Course: Main Course
Cuisine: American
Ingredients Equipment Method Notes

Ingredients
  

For the Tomahawk Prime Rib
  • 1 two bone prime rib tomahawk about 6 lbs; a regular two bone prime rib works
  • steak seasoning to taste, or kosher salt, coarse black pepper and garlic powder
For the Roasted Garlic and Onion Compound Butter
  • 1 stick unsalted butter 1/2 cup, softened
  • 1 head garlic roasted
  • 1 medium white onion finely diced
  • 1 tbsp olive oil divided between the garlic and the onion
  • 1 tbsp fresh parsley finely chopped
  • 1 tsp fresh rosemary finely chopped
  • 1 tsp fresh thyme leaves
  • 1 tsp soy sauce for the onion
  • 1/2 tsp kosher salt or to taste
  • 1/2 tsp black pepper freshly cracked

Equipment

  • Grill Set up for high heat searing, then 275°F indirect. A kamado, kettle or gas grill with a two zone setup.
  • Meat Thermometer Leave-in probe or instant read.
  • Food Processor For the compound butter.
  • Skillet For the onion.
  • Aluminum Foil For roasting the garlic.

Method
 

The Night Before
  1. Season the tomahawk heavily on all sides and edges. Set it uncovered on a wire rack in the fridge for 12 to 24 hours. If short on time, season right before cooking.
Compound Butter
  1. Cut the top off the garlic head to expose the cloves. Set on foil, drizzle with a little of the olive oil, season with salt, pepper and garlic powder, wrap tightly, and roast at 400°F in the oven, air fryer or grill for 45 to 60 minutes, until soft. Cool.
  2. Heat the remaining olive oil in a skillet over medium low. Add the diced onion and cook 10 to 15 minutes, stirring occasionally, until soft and cooked down. Add the soy sauce and cook until the liquid is gone. Cool.
  3. Add the softened butter, roasted garlic squeezed from its skins, cooled onion, parsley, rosemary, thyme, salt and pepper to a food processor. Blend until minced and even. Taste, adjust, and refrigerate in a small bowl until the steak is ready.
Grill
  1. Heat the grill to high. Sear the tomahawk on all sides and edges until a deep brown crust forms and the outside fat has rendered. Watch for flare-ups.
  2. Lower the grill to 275°F and set up for indirect heat. Move the tomahawk to the indirect side and insert a thermometer into the thickest part, away from the bone. Cook until 135°F internal for medium rare, about 2 to 4 hours total depending on thickness and starting temperature. Go by temperature, not time.
Rest and Serve
  1. Rest at least 20 minutes. Cut between the bones to separate the two steaks. Put a generous dollop of compound butter on the cut side of each and let it melt in as they rest.
  2. Flip the steaks crust side up, spoon melted compound butter over the top, and slice against the grain. Spoon more butter over the slices and serve the rest on the side for dipping.

Notes

Doneness (after resting): Rare 120 to 125°F, medium rare 130 to 135°F, medium 140 to 145°F, medium well 150 to 155°F, well done 160°F and up. Pull a few degrees early for carryover. The USDA recommends whole beef cuts reach 145°F with a 3 minute rest; medium rare is below that, so that is your call.
Forward sear: Searing first renders the outside fat on this thick, fatty cut. Reverse searing leaves the fat cap soft.
Timing: Prep time and the 3 hour cook time are estimates. The cook runs 2 to 4 hours depending on thickness and starting temperature.
Storage: Sliced steak keeps 3 to 4 days in the fridge or 2 months frozen. The butter keeps about a week in the fridge or 3 months frozen. Reheat slices covered in a 275°F oven until warm.

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