Rinse rib roast and pat dry, then remove excess fat. Not too much though, the fat will give your roast flavor.
Place thyme, rosemary, salt, peppercorns and grapeseed oil in the mortar (or bowl) and grind with pestle (or muddler).
You are not trying to grind the pepper and salt as such, but instead you want to incorporate the flavors of the ingredients.
With your hands, spread the herb mixture all over your rib roast.
Pat the herb mixture onto the rib roast to make sure it doesn't fall off during cooking.
Place rib roast in a roasting pan, fat side up, then place in a preheated oven at 450 for 15 mins.
After 15 mins the fat should have begun to crisp.
Lower oven to 350 and cook for approx. 1 3/4 hours.
Remove from oven when your rib roast registers at 145 on a meat thermometer for medium - to medium/well