Directions

1. For the oyster mushroom butter, add the olive oil to a medium sized saucepan and bring to medium-high heat.
2. Add the minced shallot and garlic to the pan and sauté for 2-3 minutes, until fragrant and lightly caramelized.
3. Add the oyster mushrooms to the pan and a pinch of salt and black pepper. Continue to sauté until tender and cooked though, about 6-8 minutes. Season to taste.
4. Remove from heat and let cool. Once cool, add to a food processor and blend until minced. Add the butter, chopped parsley, and a pinch of salt and pepper. Blend again until well incorporated. Season to taste.
5. Store butter in fridge until ready to use, then bring to room temperature.
6. For the bone in rib roast, generously season the prime rib with kosher salt and black pepper on all sides.
7. Allow prime rib to come up to room temperature, allow to stand out for about 1-2 hours, depending on big the prime rib is.
8. Set Big Green Egg or oven to 350°F indirect heat and place a drip pan underneath to catch drippings.
9. Rub prime rib down with oyster mushroom butter, reserving about 1/3 of it.
10. Place the prime rib in the center of the Egg or oven and insert meat probe in the thickest part of the meat.
11. Cook for about 2-3 hours, or until an internal temperature of 120-125°F is reached (for medium-rare doneness). *Rule of thumb is about 15 minutes cook time per pound.​​12. Remove the prime rib from the Egg/oven and lightly slather with the remaining oyster mushroom butter. Lightly tent prime rib with aluminum foil and allow to rest for 30-45 minutes. (It will continue to cook, raising the internal temperature 5-10 degrees.)13. For the Cipollini onion-oyster mushroom sauce, add olive oil to a medium sized saucepan, and bring to medium-high heat.
12. Add the onions to the pan and get a nice hard sear on both sides, about 4-5 minutes.
13. Add 2 tbsp butter to pan and baste the onions with butter until golden brown.
14. Add the garlic, oyster mushrooms, and a pinch of salt and pepper. Sauté until the mushrooms are fork tender, about 5-7 minutes.
15. Remove vegetables from the pan, add the remaining 2 tbsp butter and the flour and whisk until a blond roux forms, about 45 seconds.
16. Whisk in the beef stock, bring to a boil, and once thickened, whisk in the heavy cream, Dijon mustard, and Worcestershire sauce.
17. Reduce to a simmer and return the mushrooms and onions to the pan.
18. Simmer until the onions are fork tender, about 5-7 minute. Season to taste with salt and pepper.
19. Once the prime rib has rested, slice to desired thickness and serve with the Cipollini onion-oyster mushroom sauce spooned over the top.