Preheat oven to 260°C.
Mix together the butter, garlic, herbs, salt, and pepper in a bowl.
Rub the herb butter all over the rib roast, then place on a roasting tray with a rack.
Bake for 5 minutes 500g of meat.
Turn off the heat and let the rib roast sit in the oven for 2 hours, making sure you do not open the oven door or else the residual heat will escape.
Once the 2 hours are up, remove the roast from the pan and pour the pan drippings into a saucepan over medium heat.
Add the flour, whisking until there are no lumps, then add the beef stock, stirring and bringing the sauce to a boil.
Remove from heat and strain the sauce into a gravy dish.
Carve the prime rib into 2cm slices, then serve with the mashed potatoes, green beans, and sauce!