1 head Cauliflower, preferably orange (about 1 1/2 pounds)
2 tablespoons Extra-Virgin Olive Oil
2 small Yellow Onions, sliced 1/4 inch thick lengthwise
¾ teaspoon Kosher Salt
Pinch of Black Pepper
Zest of 1 Lemon
½ cup lightly packed Cilantro and Flat-Leaf Parsley, leaves, plus more for garnish
¼ cup Extra-Virgin Olive Oil
¼ cup raw shelled Pistachios
1 Garlic Clove, sliced
¼ teaspoon Kosher Salt
Pinch of Black Pepper
Make the cauliflower: Position a rack in the center of the oven and heat oven to 400 degrees. Trim the cauliflower, making sure the stem is cut flush with the head so it sits flat. Heat a 10-inch cast-iron or other heavy ovenproof skillet on the stove over medium heat. Add 1 tablespoon oil, the onions and 1/4 teaspoon salt and cook, stirring, until translucent and turning golden on the edges, 7 to 10 minutes. Stir in 3/4 cup water and remove from the heat.
Rub the cauliflower with the remaining tablespoon oil then with the pepper and remaining 1/2 teaspoon salt. Clear the center of the skillet and place the cauliflower in it. Cover the pan tightly with foil and place in the center of the oven. Bake until a paring knife meets no resistance when inserted into the cauliflower, 20 to 30 minutes.
Meanwhile, make the pesto: Reserve a bit of lemon zest for garnish. Place the rest in a food processor, along with the herbs, oil, pistachios, garlic, salt and pepper. Pulse until well combined.
Turn oven to 450 degrees on the regular setting or, if you have a convection option, 425 degrees. Uncover the cauliflower and baste with some of the pan juices. Cook, basting occasionally and adding 1/4 cup of water to the pan if it threatens to dry out, until nicely browned, 20 to 30 minutes more. Spoon the pesto over top, sprinkle with reserved lemon zest and more herbs, and serve.