Romesco is a classic nut-based Spanish sauce that is most often served with fish, although we find that it is also excellent for poultry, especially for braised chicken thighs that have first been browned until the skin is crispy. While romesco sauces are usually made with pine or hazelnuts, we love the creaminess of marcona almonds—a Spanish almond that is less woody in flavor than more traditional varieties.
Other hallmarks of romesco sauces are roasted tomatoes, red bell peppers and vinegars. Piment d’espelette is a mild, tasty chili pepper largely cultivated in France but which is integral to the Basque cuisine of Northern Spain. We find that it adds a mild spice that enlivens the sauce. You can certainly omit it or substitute another mild pepper if you cannot find piment d’espelette.