Wash mushrooms. Put two cups of water to boil in a medium-sized pot; add bay leaves, a piece of onion and ½ tablespoon of salt. Add mushrooms, reduce the heat to medium and close with the lid. Boil mushrooms for 15 minutes.
Slice onion, chop garlic and basil leaves. Place them in a bowl, and add apple cider vinegar, olive oil, and black pepper. Mix well all the ingredients. This mixture will make a marinade.
Turn off the heat. With a ladle, transfer the mushrooms and a cup of the mushroom broth from the pot to the bowl with the marinade. Mix well.
Close the bowl with a food wrap or a big plate. Let the mushrooms marinate for two hours at room temperature.
Meanwhile, prepare the buckwheat. If you use organic buckwheat, as we did for this recipe, roast a cup of buckwheat over medium heat until golden.
Put two cups of water to a boil in a pan. Add the roasted buckwheat and boil it for 15 minutes. Add salt to taste at the end. All the water should evaporate. Turn off the heat.
Leave the buckwheat on the stove, covered with the lid, until the marinade is ready. Ideally, you start cooking the buckwheat 30 minutes before serving, so it is fresh and warm.
Strain the marinade. Keep only the mushrooms and other ingredients, and put them in a bowl.
Now the mushrooms are ready to be served with the buckwheat. You can use the marinated onion too. We put the mushrooms around the buckwheat; however you can arrange them any way you want.