Step 1: Hydrate the shiitake mushrooms into hot water for 20-30 minutes.
Step 2: Cook the finely chopped onion, shredded carrots and chopped Apio rigs into a pan with hot olive oil, for about 4-5 minutes, then add the crushed garlic cloves, salt and smoked paprika.
Step 3: Slice the shiitake mushrooms and keep a few slices aside for decoration. You will need about 20-25 slices for the decoration, as the rest of the shiitake mushrooms will be added to the sauce along with the boletus mushrooms.
Step 4: Season with oregano, thyme and pepper, give it a mix and let it cook.
Step 5: Add the tomato paste, red wine, bay leaves, tomato sauce and vegetable soup to the pan and let it simmer for about 25-30 minutes.
Step 6: In the end, add the red lentil to the sauce and let it simmer for another 10 minutes. You can use canned lentil for a reduced cooking time.
Step 7: For the sauce, melt the butter in a hot pot, then add the flour and let it fry for a few minutes. Add the warm milk and whisk continuously, cooking the sauce for a few minutes.
Step 8: Season the sauce with salt and pepper, add the Dijon mustard and shredded cheddar and mix well until the sauce starts to thicken, then turn off the heat.
Step 9: For the assembling of the lasagna, you need to use a rectangular thermoresistant dish (approximate dimensions: 25 x 18 cm). Add a few tablespoons of sauce to the bottom of the pan and spread it evenly, then add a layer of lasagna sheets.
Step 10: On top of the lasagna sheets, add a layer of mushroom and lentil sauce, then another layer of the white sauce on top.
Step 11: Repeat the process until the tray is completely filled. Over the last layer, sprinkle cheddar cheese and decorate with shiitake mushroom slices.
Step 12: Bake the lasagna in the preheated oven at 180°C, for about 35-45 minutes, or until the cheddar cheese reaches a brown colour.