Romesco is a typical Spanish sauce which originated in Tarragona in the autonomous region of Catalunya.

As with many traditional Spanish sauces, it's thickened with bread, olive oil and ground almonds or hazelnuts, depending on the region.. Almonds were originally far more prevalent in the south and hazelnuts more common in the north.

They are mixed with roasted garlic, olive oil and and ground dried red peppers in a mortar. 

1. Roast the tomatoes and garlic in a 150° C (300° F) oven for 15 minutes; cool.
2. Soak the ñonas in water for 1 day to peel them easily and remove the flesh.
3. Halve the tomatoes and squeeze lightly to remove as many seeds as possible.
4. Place the tomatoes, garlic and peppers in a bowl and mash with a pestle to form a purée, gradually adding the powdered nuts and a little of the chile soaking water. You could also use a food processor.
5. Add the vinegar, season and emulsify with the arbequina oil.
6. Strain the sauce and refrigerate.