The easiest way to cook fingerling potatoes is on a flat cast iron griddle set directly on a hot barbecue grill. If you don’t have a griddle, a cast iron skillet will work. We like an assortment of heirloom potatoes for this recipe, but a single variety is just fine. Be sure to use potatoes of a similar size to ensure even cooking. The pesto sauce is optional, but it makes a nice drizzle and packs a flavorful punch.
Bring a large pot of water to a boil over high heat. Add 1 tablespoon of salt and the potatoes. Cook, uncovered, for 5 minutes. Drain and set aside. When the potatoes are cool enough to handle, cut them in half lengthwise. Place the potatoes in a bowl; toss with the oil and season with sea salt and pepper.
Meanwhile, preheat a large cast iron griddle or skillet on a hot barbecue grill. When the griddle is very hot, arrange the potatoes on the pan cut side down, in a single layer. It may be necessary to do this in batches depending on the size of your griddle or skillet. Cook until browned, 8 to 10 minutes. Turn the potatoes and cook until the skins are blistered in spots and the potatoes are tender, about 5 minutes.
Transfer the potatoes to a platter, drizzle lightly with the pesto, if using, and serve hot.