Peel the beetroot and chop it roughly just like the onion and garlic. Drain the cooked lentils well. Puree all the ingredients of the loaf in a food processor or with a hand blender to a relatively homogeneous mixture. However, this can still be a bit lumpy. Place on a baking sheet lined with baking paper and form a roast that is almost as long as the short side of the puff pastry. Pre-bake in the oven at 180 degrees Celsius for about 20 minutes. Let cool down.

In the meantime, finely chop the mushrooms, onions and chestnuts in the food processor. If you don't have a food processor, you can chop the ingredients very finely and after frying and cooling, chop them well again.

In a pan, fry the mushroom and chestnut mixture with some vegetable oil at medium temperature. Season with salt, pepper and thyme. Keep frying until most of the liquid has boiled away and everything has combined well. Now let the mass cool down as well.

Take the puff pastry out of the refrigerator and roll it out. Now first place a thin layer of mushroom and chestnut duxelles on the puff pastry the size of the roast. In such a way that the long side of the roast is parallel to the short side of the puff pastry. Put the beetroot roast on top. Cover the roast with the rest of the duxelles from all sides. Press everything down well. Fold the puff pastry together and seal the seam well. Cut off any excess puff pastry (can be placed on the roast as a decoration or used for other dishes).

Place the roast on a baking sheet and brush with the vegetable milk. Place in the preheated oven and bake at 200 degrees Celsius for about 45 minutes.