- With the rack in the middle position, preheat the oven to 350°F (180°C).
- Place the potatoes in a pot. Cover with cold water and season with salt. Bring to a boil. Simmer for 20 minutes or until tender. Drain. Return the potatoes to the pot. Using a potato masher, purée the potatoes with the butter, milk and rosemary. Season with salt and pepper. Set aside.
- Meanwhile, in a large skillet over medium-high heat, brown the onions in the oil, stirring regularly, until nicely caramelized, about 15 minutes. Remove from the skillet and set aside.
- In the same skillet over high heat, soften the carrots, fennel and garlic in the oil for 2 minutes. Add the lamb and cook, breaking it up with a wooden spoon, until golden. Deglaze with the wine and cook for 1 minute. Add the broth and reduce until almost dry. Season with pepper.
- Press the lamb mixture into four ¾-cup (180 ml) ramekins. Add the caramelized onions and cover with the mashed potatoes. Sprinkle with breadcrumbs. Freeze at this step, if desired. Place the ramekins on a baking sheet.
- Bake for 20 minutes. Finish cooking under the broiler, if desired. Serve with a green salad, if desired.
You can prepare the shepherd’s pie in advance. In this case, increase the cooking time to 30 minutes. If frozen, let thaw out in the refrigerator before cooking for 30 minutes.