Root Vegetable Soup

Name: Root Vegetable Soup
Ingredients: 6 tablespoons unsalted butter; 1 large onion or 2 leeks (white and light green part only), chopped; 2 to 3 celery stalks, diced; 3 garlic cloves, finely chopped; 3 rosemary or thyme branches; 2 bay leaves; 3 1/2 pounds mixed root vegetables (carrot, parsnip, celery root, turnip, rutabaga, sweet or regular potato), peeled and cut into 1-inch chunks; 2 teaspoons fine sea salt, more as needed; 1/2 teaspoon black pepper, more as needed; Juice of 1/2 lemon, more for serving; Extra-virgin olive oil; Flaky sea salt; Crushed Aleppo, Urfa or other chile flakes, optional; Grated Parmesan or pecorino, optional