Rosemary-Prime-Dijon-Rib

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 (30 ml) mustard seeds
• 2 tbsp (30 ml) fresh thyme
• 2 tbsp (30 ml) fresh rosemary
• 2 tbsp (30 ml) ground black pepper
• 5 bay leaves, crumbled
• 3 egg white
Methods :