Creamy Mushroom & Orzo Soup with Lemon & Parmesan

Heat butter and oil in a large pot over medium-high heat. Add onion, celery and carrot; cook, stirring often, until the vegetables are soft, 3 to 5 minutes. Add mushrooms, garlic, thyme and 1/2 teaspoon each salt and pepper; cook, stirring occasionally, until the mushrooms are softened, 3 to 5 minutes. Add sherry and cook, stirring constantly, until all the liquid evaporates, about 1 minute. Add broth and bring to a boil over high heat. Stir in orzo. Reduce heat to maintain a simmer; cover and cook, stirring occasionally, until the orzo is tender, about 8 minutes.

Remove from heat and stir in sour cream, lemon zest, lemon juice and the remaining 1/2 teaspoon salt and 1/4 teaspoon pepper. Serve topped with Parmesan.