In Italian, brodo means “broth.” Here, the broth is an umami-packed mixture of mushrooms, celery root, wine, chicken stock, and one of our favorite secret ingredients: Parmesan rind.
In a large pot, heat 3 tbsp. oil over medium. Add the mushrooms; season with salt and pepper. Cook, stirring occasionally, until browned, 10 minutes. Transfer to a bowl.
Add 2 tbsp. oil to the pot. Add the celery root, onion, garlic, fennel seeds, and mushroom stems; season. Cook, stirring occasionally, until beginning to brown, about 10 minutes. Add the wine. Cook over high heat, stirring often, until almost evaporated, 2 to 3 minutes. Add the stock and cheese rind. Bring to a boil. Boil until the flavors meld, about 10 minutes. Using a fine-mesh sieve, strain the broth into a saucepan.
Bring the broth to a boil. Add the tortellini and cooked mushrooms. Cook until the tortellini is al dente, about 3 minutes. Divide among bowls. Drizzle with the remaining 2 tbsp. oil. Sprinkle with the parsley.