Add the thyme, rosemary, garlic cloves, peeled shallot, 3 tablespoons of olive oil, butter, and salt and pepper to a food processor and pulse on high speed until combined and like a thick paste.
Add the potatoes to a bowl and toss with 2 tablespoons of olive oil, salt and pepper, and then add them to the pan with the rib roast and cook for 40-45 minutes.