Trim the root end off the leek. Cut the leek lengthwise into quarters and then crosswise into 1/2-inch slices. You should have about 4 cups. Transfer the slices to a bowl and wash them thoroughly in cool water, then drain.
Heat the butter and oil in a large pot over high heat. Add the leek and onion and sauté for 2 to 3 minutes, until the vegetables begin to sizzle lightly.
Meanwhile, with a sharp knife or vegetable peeler, carefully peel the tough outer skin from the butternut squash. You should have about 11/2 pounds of flesh. Remove and reserve the seeds and cut the flesh into 1/2-inch pieces. You should have about 51/2 cups.
Add the cubed squash, stock, water, and salt to the leek and onion mixture in the pot and bring to a boil. Cover, reduce the heat, and cook at a gentle boil for 15 minutes, or until the squash is tender.
Add the pastina and cook for another 5 minutes. Stir and serve immediately, garnished with the pumpkin seeds, if desired.
Serves 6
1 large leek (about 8 ounces), dark green outer leaves
and any damaged or wilted inner leaves removed and discarded
1 tablespoon unsalted butter
1 tablespoon extra virgin olive oil
1 cup coarsely chopped onion
1 butternut squash (about 21/4 pounds)
2 cups chicken stock 4 cups water
1/2 teaspoon fine sea salt, or to taste
1/2 cup pastina
1/4 cup toasted pumpkin seeds, for garnish (optional)