1 lb. fresh chestnuts (about 2 cups when shelled), divided
2 Tbsp. olive oil
1½ cups peeled, cubed butternut squash
1½ cups peeled, cubed acorn squash
2 medium carrots, peeled and chopped
1 medium yellow onion, diced
2 cups vegetable broth
2 cups chicken broth (homemade or low-sodium store-bought)
Salt and pepper to taste
1 Tbsp. butter
½ cup sliced shiitake mushrooms
2 slices prosciutto, cut into thin strips
4 to 6 tsp. sour cream
• Preheat the oven to 350 degrees. Use the tip of a sharp paring knife to make an X on the flat side of each chestnut. Roast for 20 minutes, or until the skins begin to open away from the meat.
• While the chestnuts are still warm, remove the outer shell and inner skin by placing the flat side of a chef's knife on top of each chestnut and pushing down gently; the shell will separate in half and the meat can be pulled out. Select 5 kernels to use for garnish, slice thinly and set aside. Coarsely chop the remaining chestnuts and set aside.
• Heat the oil over medium heat in a Dutch oven or stockpot. Add the butternut and acorn squash, carrots and onion, stirring occasionally until the onion is translucent. Add the vegetable broth, chicken broth, remaining roasted chestnuts, and salt and pepper. Bring to a boil then cover, lower the heat and simmer. Use a potato masher or a large wooden spoon to mash the vegetables a few times while the soup is simmering. Cook until the chestnuts are soft and mushy, about 40 to 50 minutes.
• Measure out 1½ cups of soup and set aside. Use an immersion blender or transfer the remaining soup to a blender, and purï¿½e. Return purï¿½ed soup and the reserved 1½ cups of chunky soup to a Dutch oven or stockpot. If thinner soup is desired, add broth or water. Adjust seasoning if necessary.
• Prepare the garnish by heating the butter in a small sautï¿½ pan over medium heat. Sautï¿½ the sliced mushrooms, reserved sliced chestnuts and prosciutto.
• To serve, ladle a portion of the soup into each bowl. Place 1 teaspoon of sour cream in each bowl, then divide the garnish mixture evenly among the bowls.