Classic Slow-Roasted Prime Rib with Mashed Potatoes and Creamed Spinach

This classic steakhouse-style dinner features tender, slow-roasted prime rib served with creamy mashed potatoes and rich creamed spinach. The combination is inspired by the traditional presentation associated with Lawry’s The Prime Rib, where prime rib is carved tableside and served with mashed potatoes, gravy, and creamed spinach.

This homemade version makes an impressive Sunday dinner, holiday meal, or special occasion feast.

Ingredients

For the Prime Rib

1 standing rib roast, 4–6 pounds
2 tablespoons olive oil
2 tablespoons kosher salt
1 tablespoon freshly ground black pepper
1 tablespoon garlic powder
1 teaspoon onion powder
1 teaspoon dried rosemary
1 teaspoon dried thyme

For the Mashed Potatoes

2½ pounds Yukon Gold potatoes
4 tablespoons butter
½ cup warm whole milk
¼ cup heavy cream
1 teaspoon salt
½ teaspoon black pepper

For the Creamed Spinach

1 pound fresh spinach
2 tablespoons butter
½ small onion, finely chopped
2 cloves garlic, minced
½ cup heavy cream
¼ cup grated Parmesan cheese
¼ teaspoon nutmeg
Salt and black pepper to taste

Directions

1. Prepare the Prime Rib

Remove the roast from the refrigerator about 1–2 hours before cooking to take some of the chill off.

Pat the beef completely dry with paper towels.

Rub the outside with olive oil.

Combine the salt, black pepper, garlic powder, onion powder, rosemary, and thyme. Rub the seasoning mixture generously over every surface of the roast.

2. Slow-Roast the Beef

Preheat the oven to 250°F (120°C).

Place the roast fat-side up on a rack inside a roasting pan.

Insert a meat thermometer into the thickest part of the roast, avoiding the bone.

Roast slowly until the desired internal temperature is reached.

For medium-rare, remove the roast from the oven at approximately 125–130°F (52–54°C). The temperature will rise during resting.

Cooking time varies considerably depending on the size and shape of the roast, so using a thermometer is much more reliable than relying only on time.

3. Rest the Prime Rib

Transfer the roast to a cutting board and loosely cover it with foil.

Allow it to rest for 30–45 minutes.

This gives the juices time to redistribute throughout the meat.

4. Make the Mashed Potatoes

Peel the potatoes if desired and cut them into evenly sized chunks.

Place them in a large pot, cover with cold water, and add a little salt.

Bring to a boil and cook for approximately 15–20 minutes, or until fork-tender.

Drain thoroughly.

Return the potatoes to the warm pot and mash with the butter, warm milk, and heavy cream.

Season with salt and black pepper.

For exceptionally smooth potatoes, whip them gently with a hand mixer, being careful not to overmix.

5. Prepare the Creamed Spinach

Wash the spinach thoroughly.

Heat butter in a large skillet over medium heat.

Add the chopped onion and cook for 3–4 minutes until softened.

Add the garlic and cook for another 30 seconds.

Add the spinach in batches and cook until wilted.

Reduce the heat and stir in the heavy cream, Parmesan, nutmeg, salt, and pepper.

Simmer gently for 3–5 minutes, until creamy and slightly thickened.

6. Finish the Prime Rib

For a beautifully browned crust, increase the oven temperature to 500°F (260°C).

Return the rested roast to the oven for approximately 5–10 minutes, watching carefully until the exterior becomes deeply browned.

Remove and let it rest briefly before carving.

7. Carve and Serve

Slice the prime rib against the grain into your preferred thickness.

Arrange the beef on warm plates alongside generous portions of whipped mashed potatoes and creamed spinach.

Serve with beef au jus and horseradish cream for the classic steakhouse experience. Lawry’s traditionally serves its prime rib with au jus and horseradish, along with mashed potatoes and creamed spinach or other classic sides.

Tips for Perfect Prime Rib

Use a meat thermometer: Internal temperature is the best indicator of doneness.
Season generously: A large roast needs plenty of seasoning.
Don’t skip resting: Resting helps keep the slices juicy.
Slice against the grain: This produces more tender bites.
Warm the serving plates: It helps keep the meat and sides hot.
Make the sides while the roast rests: This makes timing the entire meal easier.

Storage

Store leftover prime rib in an airtight container in the refrigerator for 3–4 days.

For best results, reheat slices gently in a low oven with a little au jus or beef broth to prevent them from drying out.

Mashed potatoes and creamed spinach can also be refrigerated for several days and reheated gently.

Recipe at a Glance

Prep Time: 30 minutes
Roasting Time: Varies by roast size and desired doneness
Resting Time: 30–45 minutes
Servings: 6–8
Difficulty: Intermediate

Meta Description

Make a classic slow-roasted prime rib dinner with tender beef, creamy whipped mashed potatoes, and rich creamed spinach. A delicious steakhouse-style meal perfect for holidays and special occasions.