Preheat your oven to 450°F (232°C).

In a dry skillet over medium heat, toast the coriander seeds until fragrant, about 2-3 minutes. Let cool, then grind them in a spice grinder or mortar and pestle.

In a bowl, combine the ground coriander, smoked paprika, kosher salt, black pepper, and minced garlic. Add the olive oil to form a paste.

Rub the spice mixture all over the prime rib roast, ensuring it is evenly coated. Let the roast sit at room temperature for about 30 minutes to 1 hour.

Place the seasoned prime rib on a rack in a roasting pan. Roast in the preheated oven for 20 minutes. Then, reduce the temperature to 325°F (163°C) and continue roasting until the internal temperature reaches your desired doneness (125°F for rare, 135°F for medium-rare, 145°F for medium). This will take about 1.5 to 2 hours, depending on the size of the roast.

While the roast is cooking, melt 2 tablespoons of the butter in a skillet over medium heat. Add the sliced leeks and cook slowly until they are soft and caramelized, about 15-20 minutes. Stir in the honey and fresh thyme, and season with salt and pepper to taste. Remove from heat and let cool slightly.

In a mixing bowl, combine the remaining 2 tablespoons of softened butter with the cooled caramelized leek mixture. Mix until well combined.

Once the prime rib reaches the desired temperature, remove it from the oven and let it rest for at least 20 minutes before slicing. This allows the juices to redistribute.

Slice the roast and serve with a generous dollop of the caramelized leek confit butter on top.