Butternut Squash and Sweet Potato Soup

Ingredients

• 2 tablespoons olive oil
• 2 small onions, chopped
• 2 celery ribs, chopped
• 2 medium carrots, chopped
• 1 medium butternut squash (3 pounds), peeled, seeded and cut into 1-inch cubes
• 1 medium sweet potato (about 8 ounces), peeled and cut into 1-inch cubes
• 1 yellow summer squash, halved lengthwise and sliced
• 4 garlic cloves, minced
• 4 cups vegetable broth
• 2 teaspoons dried savory or herbes de Provence
• 1/4 teaspoon pepper
• Grated Parmesan cheese, optional