We've tasted arugula pesto, which is quite bitter and works much better in rich soups than on simple pastas, and we've discovered several recipes for pestos made with other herbs. One of these from the region of Castelnuovo Magra in eastern Liguria, adds marjoram and parsley to the basil, extending the traditional herb rather than replacing it. Another version, actually a pistou from Menton, just across the French border, uses only marjoram. Such sauces can be quite good, but they are rarities these days—far more likely to be encountered in cookbooks than in real life. In fact, when we asked a culinary historian from Castelnuovo about the mixed-herb pesto, he responded, in mild shock, "But we use only basil in our pesto. It's the best!"