Lentil Shepherd's Pie

Steps

1. Finely chop the mushrooms, by hand or with short pulses in a food processor, into pieces about the size of a lentil. Cut the carrots, onion and celery into 1/4-inch (5 mm) dice and mince the garlic. Rinse and drain the green lentils.
2. Peel the potatoes, cut them into even 2-inch (5 cm) chunks and put them in a large pot with 2.5 l of cold water and the coarse salt. Bring to a simmer and cook for 20 to 25 minutes, until a knife slides in with no resistance.
3. Meanwhile, heat 2 tbsp of olive oil over high heat in a Dutch oven. Add the chopped mushrooms and cook for 8 minutes, stirring often: they release their water, it evaporates, then they brown and leave a dark crust on the bottom of the pot.
4. Lower the heat to medium and add the last tbsp of oil with the carrots, onion and celery. Cook for 6 minutes, scraping the bottom, until the onion is translucent. Add the garlic and tomato paste and stir for 2 minutes, until the paste darkens.
5. Pour in the red wine, scrape up the brown bits and reduce for 2 minutes. Add the lentils, vegetable broth, thyme and bay leaf. Bring to a boil, then simmer over low heat with the lid ajar for 30 to 35 minutes, stirring now and then, until the lentils are tender and the liquid is almost absorbed: the mixture should be moist, not soupy.
6. Preheat the oven to 400°F (200°C). Remove the thyme and bay leaf from the lentils, stir in the soy sauce and black pepper, taste and add up to 1/2 tsp of fine salt only if needed, since the soy sauce is already salty.
7. Drain the potatoes and return them to the pot over the heat for 1 minute to dry out. Mash them with a potato masher or ricer, work in 70 g of butter, then the hot milk a little at a time, using a spatula. Grate in the nutmeg and season with 1.5 tsp of fine salt. Off the heat, beat in the egg yolks one at a time.
8. Spread the lentils in a 12 x 9-inch (30 x 22 cm) baking dish. Drop the mash on top in large spoonfuls, starting at the edges so it doesn't sink, then smooth it out and rake deep ridges across it with a fork. Scatter the shredded emmental and the remaining 10 g of butter in small pieces over the top.
9. Bake for 25 minutes at 400°F (200°C), until the ridges are deep golden and the edges are bubbling. Let it rest for 10 minutes before serving so the portions hold together.