Season both sides of each steak with one teaspoon of the spice rub.

Marinate the steaks overnight in the fridge.

Remove from fridge and allow steaks to reach room temperature before grilling.

Grill 45 minutes on each side. Use a meat thermometer to check the temperature for your desired results. (See note.) After grilling, set steaks aside.

Fill a pot of water and add the celery root and potatoes. Bring the water to a boil and then lower the heat to medium-low.

Continue to cook the vegetables in the water until they are soft enough to be pierced with a fork.

Heat one tablespoon of oil in a medium-sized frying pan. Add the onion and sauté on low until golden.

Drain the cooking liquid from the pot, reserving half a cup of liquid in a separate bowl.

Mash celery root and potatoes until creamy. Add one tablespoon oil and then one tablespoon cooking liquid at a time, mixing until a thick, creamy texture is achieved. Once you achieve the texture you want, discard the rest of the liquid.

Add the sautéed onions and season with salt and pepper to taste.

Preheat oven to 375 degrees Fahrenheit (190 degrees Celsius).

Spread grape tomatoes on a parchment-lined baking sheet. Spray or drizzle with oil and season with spice rub.

Roast in the oven for 20-25 minutes.