Step 1

Preheat oven to 450 degrees. Cut pumpkin into 2-inch pieces. Combine pumpkin, onion, mushrooms, and garlic on a rimmed baking sheet. Add oil and 2 teaspoons salt; toss to coat, then spread in a single layer. Roast until pumpkin is tender when pierced with the tip of a sharp knife, about 30 minutes, rotating pan and tossing vegetables halfway through. Let cool, then remove skins.

Step 2

Transfer vegetables to a medium saucepan; heat over medium. Pour in 2 cups stock; puree with an immersion blender until smooth. With the blender running, slowly add remaining 3 cups stock, and puree until smooth. Bring soup just to a simmer. Remove from heat, and season with salt and pepper. Cover to keep warm.