Sauté onion, carrot & celery in olive oil with salt + pepper until softened in a large pot
Add pasta, toast 1–2 min until lightly golden, then toss in mushrooms
Pour in chicken stock to cover by ~1 inch. Simmer like risotto, adding more stock/water as needed
When pasta is just shy of al dente, stir in butter, spinach & splash of vinegar
Serve topped with Parmigiano Reggiano
