Season the pork chops on both sides with the fennel seeds and a few pinches each of salt and pepper. Set aside while you prepare the vegetables.
Melt the butter in a large wide pot or Dutch oven over medium heat. Add the lemon zest strips, garlic and rosemary and cook, stirring, until the garlic is softened, 1 to 2 minutes. Stir in the leeks, sliced fennel, 1/2 teaspoon salt and a few grinds of pepper. Pour in the cider, cover and reduce the heat to medium low. Cook, stirring occasionally, until the leeks and fennel are tender but not browned, 15 to 20 minutes.
Meanwhile, heat the olive oil in a large skillet over medium-high heat. Working in two batches if necessary, add the pork chops and cook until well browned but still rosy near the bone, 4 to 5 minutes per side. Transfer to a plate and let rest 5 minutes.
Discard the rosemary from the leeks and stir in the lemon juice and 1/4 cup fennel fronds; season with salt and pepper. Divide among plates and top with the pork. Drizzle with any accumulated juices from the pork plate and sprinkle with a few more fennel fronds.