Romesco sauce is a Spanish staple made from roasted red peppers, tomatoes, and garlic that is served over fish, pasta, spaghetti squash, or a dip for bread.
Move oven rack to middle of oven and preheat to 400° F (205° C).
Place red peppers, garlic and tomatoes on a baking sheet and bake for 40 minutes until fully roasted (may need to remove garlic early if the cloves are small).
Remove pan from oven. Use tongs to put red peppers into a paper bag to soften the skin and make it easier to remove.
When the tomatoes and garlic are cool enough to handle, peel and core tomato and peel garlic. Place in food processor along with pistachios, vinegar, oil, and paprika. Peel red pepper skins off and place in food processor as well. Mix well. Season with salt and pepper to taste and pulse to mix in.
Serve over chicken, fish, pasta or spaghetti squash, or simply use as a dipping sauce for crusty bread.