Begin by rinsing the lentils and then cooking them in vegetable broth over medium heat until tender, about 20-25 minutes. Once done, drain any excess liquid and set aside.
1 cup dried lentils, 3 cups vegetable broth
While the lentils cook, peel and chop the sweet potatoes into chunks. Place them in a large pot and cover with water, then bring to a boil and cook until very soft, about 15 minutes.
2 large sweet potatoes
In a Dutch oven or large skillet, heat olive oil over medium heat. Add diced carrot, celery, and minced garlic, sautéing until the vegetables soften and become fragrant, about 5 minutes.
1 large carrot, 1 stalk celery, 2 cloves garlic, 2 tablespoons olive oil
Add tomato paste, chopped sage, thyme, salt, and pepper to the vegetables, stirring to combine. Cook for another 2 minutes until aromatic.
2 teaspoons fresh sage, 1 teaspoon dried thyme, 1 tablespoon tomato paste
Stir the cooked lentils into the vegetable mixture, mixing well. Let it simmer for 5 minutes to meld the flavors and thicken slightly.
1 cup dried lentils, 2 tablespoons olive oil
Drain the soft sweet potatoes and return them to the hot pot. Mash thoroughly using a potato masher until smooth. Mix in chopped sage and season with salt and pepper as needed.
2 large sweet potatoes, 2 teaspoons fresh sage
Preheat your oven to 375°F (190°C). Spread the lentil vegetable mixture evenly in a baking dish.
Top the lentil filling with the smooth sweet potato mash, spreading it out with a spatula for an even layer. Use a fork to create ridges on top if you like a textured crust.
Bake uncovered in the preheated oven for about 20-25 minutes, until the topping is golden and slightly crispy around the edges.
Remove from oven and let it rest for 5 minutes before serving. Slice into portions and enjoy the hearty, comforting layers of this fall-inspired shepherd's pie.
