Root Vegetable Soup

unsalted butter

large onion or 2 leeks (white and light green part only), chopped

to 3 celery stalks, diced

garlic cloves, finely chopped

rosemary or thyme branches

bay leaves

mixed root vegetables (carrot, parsnip, celery root, turnip, rutabaga, sweet or regular potato), peeled and cut into 1-inch chunks

fine sea salt, more as needed

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