Add all ingredients and blend in a food processor or blender until fully incorporated and smooth; season to taste with salt and pepper.

Set aside until ready to use; reserve 2 tablespoons pesto for broken spaghetti.

Add olive oil to large saucepan and bring to medium-high heat.

Add onions and sauté for 30 seconds until lightly brown and fragrant.

Add grape tomatoes and pinch of salt, pepper, and crushed red pepper and sauté until slightly blistered; about 90 seconds to 2 minutes. Carefully press down and mash tomatoes.

Add garlic and lightly sauté for 15 seconds, then add chicken stock and reduce by half in volume; about 1 minute.

Add pesto and heavy cream, stir until well incorporated and beginning to boil; reduce to medium heat and cook until slightly thickened; about 1 minute.

Add spaghetti and basil to pan and toss all together until well coated.

Add Parmesan cheese and toss until sauce thickens to cheese sauce-like consistency. Season to taste with salt and pepper.

Thaw Chateaubriand in refrigerator for 24 to 48 hours.

Remove from refrigerator and pat dry all over with paper towels.

With the short end facing toward you, use a sharp chef’s knife to make a 1” incision along the long side of the Chateaubriand.

Continuously and carefully, make 1” incisions along the seam on the inside of the cut, rolling the Chateaubriand out until it’s butterflied and 1” in thickness; press flat with hands.

Using half of spinach pesto, coat a thin layer inside butterflied Chateaubriand, leaving a 1” border without pesto.

Carefully roll Chateaubriand up from the long end without spilling pesto, then tie off every 2” with the 8 pieces of butcher's twine, spacing evenly and double knotting them, then trim excess twine.

Rub down with 2 tablespoons olive oil and season generously with salt and pepper, then leave on counter and bring to room temperature over about 30 minutes.

Preheat oven to 250 degrees Fahrenheit.

Once oven is preheated, place stuffed Chateaubriand on roasting rack and put on center rack of oven, then cook for about 45 minutes until internal temperature reaches 115 degrees Fahrenheit for rare doneness. Refer to Omaha Steaks cooking chart to achieve a different level of doneness.

Add grapeseed oil to an extra-large cast-iron pan and bring to medium-high heat. Sear Chateaubriand on all sides until browned for about 45 seconds on each side; once all sides are browned, add butter and butter-baste on each side for about 15 seconds.

Rest Chateaubriand for 15 to 20 minutes. Once rested, use butcher’s twine as a guide to cut each slice so the twine is in the center.

Take remaining unused pesto and whisk with 1/4 cup olive oil to thin it out, then season to taste with salt and pepper and use for final plating.

Plating: Place broken spaghetti in center of plate, top with one Chateaubriand slice, and finish with thinned out spinach pesto.