First, rinse the lentils and place them in a pot with three times their volume of cold water (unsalted). Add 2 bay leaves and a generous pinch of thyme. Bring to a boil, then cover and simmer for about 25 minutes.

Meanwhile, peel the sweet potatoes and russet potatoes. Cut them into pieces to speed up cooking. Place them in a pot of simmering salted water and cook for about 20 minutes. When they're tender, mash them with a potato masher, adding the vegan butter, a little cooking water, salt, and pepper to taste. Be careful not to add too much water—you want a smooth, firm texture.

Now prepare the mushrooms. Wipe them clean, peel if needed, and slice thinly. Do the same with the onion and garlic. In a large pot, sauté the sliced onion and garlic over low heat. Add the mushrooms and a splash of sweet soy sauce. Cook, stirring, for 5 minutes, then add the cooked lentils. Season with salt, Espelette pepper, and thyme. Simmer everything together for 5 minutes, then set aside.

Roughly chop the hazelnuts with a knife. Lightly dress the arugula with your favorite vinaigrette, then you're ready to assemble.

Place a large ring mold in the center of a plate. Fill halfway with the lentil mixture, pressing down gently. Add the sweet potato mash up to the top of the ring and smooth the surface. Gently add some arugula on top. Grate a little vegan parmesan over the arugula and sprinkle with the chopped hazelnuts. Remove the ring and serve immediately!