An abundance of mustard seeds grows in California's Napa Valley—as it does in the south of France; the regions share a similar climate. It makes sense, then, that many of the same ingredients feature prominently in both cuisines. These potatoes, grilled with a mustardy aioli (basically, garlic-scented mayonnaise) and served with a scattering of herbs, would be at home on either region's table. Delicate parsley, chives, and tarragon are known collectively as fines herbes and are a staple of Mediterranean cooking.