1. Make the romesco sauce: Preheat the oven to 300°. Season the tomatoes and peppers with 2 tablespoons of the olive oil, salt and pepper and place on a baking sheet. Slice the top of the head of garlic off, leaving the root intact. Season with salt, pepper and ½ tablespoon of olive oil. Wrap the garlic in foil and bake, along with the tomatoes and the peppers, until the garlic is soft, the tomatoes have begun to caramelize and the peppers are tender and beginning to blister, about 1 hour. Remove from the oven, cover the peppers with foil and set aside for 10 minutes, then peel the skin and remove the seeds and veins from the peppers.
2. In a small skillet set over medium heat, toast the almonds and hazelnuts with 1 teaspoon of the olive oil and salt.
3. Remove the garlic cloves from their skins. In a food processor, combine the tomatoes, peppers, garlic, toasted nuts and bread. Slowly drizzle in the remaining ¾ cup of olive oil until the mixture forms a smooth paste. Season with red wine vinegar, salt and pepper and set aside.
4. Make the steak: Season the steak with salt and pepper. Heat a cast-iron skillet set over medium-high heat. Once the pan is hot, add the 2 tablespoons of olive oil. Carefully add the skirt steak to the pan, being careful not to splash the hot oil out of the pan. Sear the steak on one side for 1 minute. Turn the steak over and sear for 1 additional minute. Add the butter, garlic and thyme to the pan and use a pastry brush to baste the steak for 2 to 3 minutes or until the steak is medium-rare. Remove the steak from the pan, cover with foil and set aside to rest for 2 to 3 minutes. Cut the steak across the grain into ½-inch slices and serve immediately with the romesco sauce.