Curried-Squash and Red-Lentil Soup

Heat oil with butter in a large heavy pot over medium heat until foam subsides, then cook squash, onion, carrot, celery, garlic, ginger, and 1 teaspoon salt, stirring occasionally, until vegetables are softened and beginning to brown, 15 to 20 minutes.

Stir in curry powder and 1/4 teaspoon pepper and cook, stirring frequently, 2 minutes.

Add lentils and water and simmer, covered, until lentils are tender, 25 to 40 minutes. Stir in lemon juice and season with salt and pepper.

Purée cilantro, oil, and 1/2 teaspoon salt in a blender.

Serve soup drizzled with cilantro oil.

Soup, without cilantro oil, can be made 3 days ahead and chilled.