Step 1

Preheat the oven to 400°F (204°C). Adjust the oven rack to the middle position. Take the pork out of the refrigerator and let it rest on the counter while the oven heats.

Step 2

Cut each onion into quarters. Cut each apple in half from top to bottom. Using a teaspoon-size measuring spoon, a melon baller, or a paring knife, trim the apple core and stem. Place each apple half, cut side down, on the cutting board and cut it in half again.

Step 3

Place the onions and apples on a rimmed baking sheet lined with foil. Drizzle the onions and apples with 2 tablespoons oil and sprinkle with 1/2 teaspoon salt and 1/4 teaspoon pepper (about 12 turns if you're using freshly cracked pepper from a pepper mill). Toss everything together with your hands and spread in a single layer.

Step 4

Mince the garlic and toss it in a small bowl along with the thyme, fennel seeds, the remaining 1 tablespoon oil, 1/2 teaspoon salt, and 1/4 teaspoon pepper.

Step 5

Pat the pork dry. Place it, fat side up, in the middle of the baking sheet, pushing the apples and onions aside. Rub the entire pork loin with the garlic mixture.

Step 6

Roast everything until an instant-read thermometer inserted in the center of the pork loin reads 145°F (63°C), 45 to 60 minutes. (You'll probably want to start checking the pork loin after 30 minutes, just to be safe.)

Step 7

Transfer the roast pork loin to a cutting board and let it rest for 5 minutes before slicing. Serve it along with the roasted apples and onions.