Rinse the buckwheat groats thoroughly under cold running water, then drain them completely.

In a large soup pot, toast the buckwheat over medium heat for 3 to 4 minutes without oil, stirring constantly, until they smell nutty and fragrant, then transfer to a bowl and set aside.

Heat the olive oil in the same pot over medium heat, add the diced onion, and sauté for 5 minutes until soft and translucent.

Add the minced garlic and sliced cremini mushrooms to the pot, cooking for 6 to 8 minutes until the mushrooms release their moisture and turn a rich golden brown.

Pour in the vegetable broth, add the toasted buckwheat groats, dried bay leaf, salt, and black pepper, then bring the mixture to a boil over high heat.

Reduce the heat to low, cover the pot with a lid, and simmer for 15 minutes until the buckwheat groats are tender and cooked through.

Discard the bay leaf, ladle the hot soup into bowls, and serve immediately topped with fresh dill and a dollop of sour cream.