Preparation

Preheat the oven to 230°C (450°F).
Place the onion slices on the bottom of a baking dish. Put aside.
Spread rib evenly with mustard.Put aside.
In a large bowl, combine salt, horseradish, mustard seeds, thyme, rosemary, pepper and bay leaves. Add the egg whites and stir until the mixture resembles wet sand. Press the salt mixture evenly onto the fat side and ends of the rib, then place the piece of meat, bone side down, on top of the onions in the roasting pan.

Roast for 15 minutes.Reduce oven temperature to 325°F (160°C) and continue cooking for 20 minutes per pound (450 g) or until an instant-read thermometer inserted into thickest part of roast reads 130°F (55°C). displays. , so that the meat is cooked medium-rare.
Place the rib roast on a cutting board and let it rest for 20 minutes. Remove and discard the salt crust before cutting into the meat.
Have fun!