Discard green top from leek; cut white portion of leek into thin slices.
Sauté leek and next 4 ingredients in hot oil in a Dutch oven over medium heat 10 to 15 minutes or until tender.
Stir in butternut squash and chicken broth; bring to a boil. Reduce heat, and simmer 30 minutes or until squash is tender. Cool slightly.
Process squash mixture, in batches, in a food processor or blender until smooth. Return to Dutch oven; stir in half-and-half, salt, and pepper.
Cook mixture over medium heat, stirring often, until thoroughly heated. Serve soup immediately.
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