2 tablespoons unsalted butter
1 cup onion, chopped
1 cup leeks, chopped (white and pale green parts only)
2 celery stalks, chopped
2 large garlic gloves, minced
2 pounds Jerusalem artichokes, peeled and cubed
1 quart chicken or vegetable stock
Shelled pumpkin seeds, toasted
Salt and pepper to taste
Serves 4