Begin by heating the vegetable broth in a saucepan over medium heat until simmering, then reduce heat to low to keep warm.
Heat olive oil in a large skillet over medium heat. Add the chopped onion and cook until translucent, about 3-4 minutes.
Stir in the minced garlic and sliced mushrooms, cooking until the mushrooms are soft and browned, approximately 5 minutes.
Mix in the buckwheat groats, stirring constantly to toast for 2 minutes, ensuring they're well-coated with the oil and vegetables.
Pour in the white wine and cook until the liquid is absorbed, about 2 minutes.
Ladle in the warm vegetable broth, one cup at a time, stirring frequently. Wait until each addition is almost fully absorbed before adding the next.
Continue this process until the buckwheat is tender and creamy, which should take about 20 minutes.
Remove from heat and stir in the grated Parmesan cheese and chopped parsley. Season with salt and pepper to taste.
Serve the risotto warm, with a dollop of sour cream on top if desired.