Lentil and sweet potato shepherd's pie

Ingredients

0 of 21 out on the counter

• 1 tbsp olive oil, for the filling
• 1 large onion, diced
• 2 medium carrots, diced
• 2 medium stalks celery, diced
• 8 oz white mushrooms, sliced
• 1 tsp garlic powder
• 2 tsp dried thyme leaves
• 1 tsp smoked paprika
• 2 tbsp no-salt-added tomato paste
• 1 cup dry green or brown lentils, rinsed
• 1 cup frozen peas
• 1 tbsp cider vinegar
• ½ tsp salt, for the filling
• ½ tsp black pepper, for the filling
• 680 g sweet potatoes, peeled (about 1¾ lb before peeling, our kitchen estimate), cut in 1-inch chunks
• ¼ cup skim milk
• 1 tbsp olive oil, mashed into the topping
• ½ tsp salt, for the topping
• 1 tsp olive oil, brushed on top
• 3 cups water, for cooking the lentils
• 1 inch of water, for steaming the potatoes

All set! Everything is out. Time to bake.

Method

1. 1Peel the sweet potatoes and cut them in 1-inch chunks. Set them in a steamer basket over 1 inch of water, cover, and steam 25 to 30 minutes, until a fork slides in with no push. Water boils near 203 °F at 5,300 ft, so allow a quarter longer than the usual 20.
2. 2While the potatoes steam, heat the 1 tbsp of oil in a deep 12-inch skillet over medium heat. Cook the onion, carrots and celery for 6 minutes, until the onion is soft. Add the mushrooms and cook 6 minutes more, until their liquid has cooked away.
3. 3Stir in the garlic powder, thyme, paprika and tomato paste. Cook 1 minute, until the paste darkens a shade. Add the lentils and 3 cups of water. Stir, scraping up anything stuck.
4. 4Bring to a boil, turn down to a steady simmer, and cover with the lid cracked. Cook 40 minutes instead of the usual 30 (simmered food takes about a quarter longer here), stirring every 10 minutes. It is done when the lentils are tender and the pan holds a thick stew with no loose water. If it is still wet, simmer uncovered 5 minutes.
5. 5Heat the oven to 425 °F; oven temperatures are not changed by altitude. Stir the peas, vinegar, ½ tsp salt and the pepper into the lentils. Spoon the filling into a 9-by-13-inch baking dish and smooth it level.
6. 6Mash the steamed sweet potato with the 1 tbsp of oil, the skim milk and ½ tsp salt until smooth. Spoon it over the filling in dollops and spread it to the edges. Rake the top with a fork and brush with the 1 tsp of oil.
7. 7Bake on the middle rack 25 minutes, until the edges bubble and the ridges are browned. The filling should read 165 °F in the center. Rest 10 minutes; it firms as it cools.
8. 8Cool leftovers no more than 2 hours, then refrigerate. Reheat portions to 165 °F, in a 350 °F oven or the microwave.