Preheat your oven to 450°F (230°C).

In a spice grinder or mortar and pestle, grind the toasted coriander seeds until fine.

In a small bowl, mix together the ground coriander, smoked paprika, garlic powder, onion powder, salt, and black pepper.

Rub the prime rib with olive oil, then coat it evenly with the spice mixture.

Place the seasoned prime rib on a roasting rack in a roasting pan.

Roast in the preheated oven for 20 minutes to develop a crust.

Reduce the oven temperature to 325°F (165°C) and continue roasting for about 1.5 to 2 hours, or until the internal temperature reaches your desired doneness (130°F for medium-rare, 140°F for medium).

Remove from the oven, tent with foil, and let it rest for at least 20 minutes before slicing.

While the prime rib is resting, melt the butter in a large skillet over medium heat.

Add the sliced leeks and salt, cooking until softened and caramelized, about 15-20 minutes, stirring occasionally.

Stir in the black pepper, thyme leaves, and lemon zest. Remove from heat and set aside.

Slice the prime rib to your desired thickness and serve with the caramelized leek butter drizzled on top.