Prepare the Vegetables:

Coarsely chop mushrooms with a knife or pulse in a food processor (work in 3–4 batches if needed).

Chop onion, carrots, and celery with a knife or pulse in the food processor.

Make the Flavor Base:

Heat olive oil in a large skillet or Dutch oven over medium heat.

Add chopped onion, carrots, and celery; sauté for 5 minutes, stirring often.

Stir in garlic, rosemary, bay leaves, and tomato paste. Cook for 3 more minutes, until tomato paste darkens.

Cook the Mushrooms:

Add mushrooms, salt, and black pepper. Cook over medium-high heat for ~20 minutes, or until mushroom liquid has evaporated and sauce is thick.

Stir in balsamic vinegar. Taste and adjust seasoning.

Cook Pasta & Combine:

Cook pasta in salted boiling water until al dente. Reserve 1 cup of pasta water, then drain.

Add pasta to the mushroom ragu with ¼ cup of pasta water. Toss over medium heat until well combined.

Serve:

Garnish with fresh basil, a drizzle of olive oil, and Parmesan cheese if desired.