Remove the prime rib from the refrigerator 2 hours before roasting to reach room temperature. Pat the roast dry with paper towels. This promotes even cooking and better browning.

Season

In a small bowl, combine kosher salt, freshly ground black pepper, minced garlic and chopped rosemary. Rub olive oil evenly over the entire surface of the roast, then press the seasoning mixture all over the roast so it adheres. Make sure to season the sides and ends.

Roast - initial high heat

Preheat oven to 475°F (245°C). Place the roast, fat cap up, on a rack in a roasting pan. Insert an oven-safe meat thermometer into the thickest part of the roast without touching bone. Roast at 475°F for 15 minutes to develop a crust.

Roast - lower temperature

Reduce oven temperature to 325°F (160°C) and continue roasting until internal temperature reaches 120°F (49°C) for rare, about 12–15 minutes per pound (for a 4 lb roast this is roughly 48–60 minutes), or adjust to your preferred doneness: 125°F (52°C) for medium-rare, 135°F (57°C) for medium. Check temperature periodically.

Rest and carve

Remove the roast from the oven when it reaches target temperature, tent loosely with foil, and let rest for 20–25 minutes. Carryover cooking will raise the internal temperature several degrees. Transfer to a cutting board and carve into 1/4–1/2 inch thick slices.

Horseradish Sauce

While the roast rests, combine the drained prepared horseradish, crème fraîche (or sour cream), mayonnaise, white wine vinegar, Dijon mustard, chopped chives, sea salt, black pepper and lemon juice (if using) in a small bowl. Stir until smooth and taste; adjust salt, horseradish or lemon to balance heat and acidity. Chill briefly if you prefer it cold.

Dinner Rolls

Warm and finish rolls

Preheat oven to 350°F (175°C) while the roast rests (or use the residual heat once the roast is out). Arrange split rolls cut-side up on a baking sheet. Brush the cut sides lightly with melted butter. Toast in the oven 5–7 minutes until warm and edges are lightly golden. Remove and sprinkle a pinch of coarse sea salt and chopped parsley on each roll if desired.

Assemble serving

Place carved prime rib slices on a serving platter. Serve warm buttered rolls alongside small bowls of horseradish sauce for guests to spread or dip. For a roll sandwich, spoon horseradish sauce onto the roll, top with a slice of prime rib and enjoy.