Position a rack in the center of the oven and heat the oven to 325°F.
Heat 2 Tbs. of the oil in a heavy-duty 12-inch skillet over medium-high heat. Add half the fennel, cut side down. Cook undisturbed until browned in spots, about 2 minutes. Flip and repeat on the other cut sides.
Arrange the fennel browned sides up in a large (10x14-inch) gratin or shallow baking dish. Add the remaining 1 Tbs. oil to the skillet and repeat with the remaining fennel. Lower the heat to medium if any smoking occurs. It’s OK if the wedges are snug in the baking dish; they’ll shrink as they braise.
Add the garlic to the skillet and and cook until fragrant, about 30 seconds. Add the wine and scrape the bottom of the pan with a wooden spoon to dissolve any browned bits, about 1 minute. Add the broth and simmer to meld the flavors, about 2 minutes. Pour over the fennel.
With a vegetable peeler, remove three 3-inch strips of zest from the orange and then juice the orange. Nestle the pieces of zest in the fennel and pour the juice over. Sprinkle with the fennel seeds, coriander seeds, 1 tsp. salt, and a few grinds of pepper.
Cover the dish tightly with foil and braise in the oven until the fennel has collapsed and a paring knife penetrates the cores with no resistance, about 1-1/4 hours.
Spoon some braising liquid over the fennel, garnish with the reserved fronds, and serve hot, warm, or at room temperature.
The fennel may be made 2 days ahead of serving.
Uncover and cool to room temperature before refrigerating it (covered).
Let the fennel come to room temperature before serving. Or reheat it, covered, in a 325°F oven.