Mushroom Yogurt Soup

So I got a new immersion blender and immediately started playing around with it. One of the first actual recipes I made was a modified cream of mushroom soup. There are plenty of mushrooms in China (you can get them at the Asian supermarkets in the States as well), so I decided to use a nice mix.

Ingredients
1/4 cup enoki mushrooms, chopped
1/4 cup shiitake mushrooms, chopped
1/4 cup oyster mushrooms, chopped
1/4 medium yellow onion, sliced
1/2 cup plain yogurt
1 bay leaf
salt
white pepper

Optional
2 Tbsp butter
flour

Saute the onion with some olive oil in a medium saucepan. Add the mushrooms and saute until mushrooms start to brown and release water. Cover with chicken stock, add some salt, pepper, and the bay leaf, and simmer for 10-12min. Remove the bay leaf and blend with immersion blender. Return the bay leaf.

Optional: In another skillet, make a roux by melting the butter and stirring in flour until it becomes a thick, smooth paste that separates from the pan easily. Add to the soup.

Simmer for another 20min or so, stirring or whisking to mix the roux in and thicken the soup. Remove from heat and add the yogurt (don't add it to the heat directly or it might curdle). Season to taste.