Preheat oven to 450°F. Cut pumpkin into 2-inch pieces. Combine pumpkin, onion, and garlic on a rimmed baking sheet. Add olive oil and salt; toss to coat, then spread in a single layer.
STEP 2
Roast until pumpkin is tender, about 30 minutes. Rotate pan and toss halfway through. Let cool and remove skins.
STEP 3
Transfer vegetables to a medium saucepan; heat over medium. Pour in 2 cups of vegetable stock.
STEP 4
Use an immersion blender to puree until smooth, adding remaining stock slowly.
STEP 5
Bring soup just to a simmer. Season with salt and pepper. Cover to keep warm until serving.