*Ingredients

2 white onions, cut to 1-inch (2.5 cm) slice
¼ c Dijon mustard
1 prime rib (about 6 lbs/2.7 kg)
1 1/2 cups (375 ml) kosher salt
⅓ c ( 75 mL ) prepared horseradish
2 tbsp. 2 tbsp (30 ml) mustard seeds
2 tbsp. 2 tbsp (30 ml) fresh thyme
2 tbsp. 2 tbsp (30 ml) fresh rosemary
2 tbsp. 2 tbsp (30 ml) ground black pepper
5 bay leaves, crumbled
3 egg white

* Methods :

Preheat oven 450°F (230°C).
Place the onion slices in the bottom of a roasting pan. Put aside.