Bring a large pot of salted water to a boil. Cook pasta according to package directions, adding the broccoli during the last 5 minutes of cooking. Drain and reserve 1 cup of pasta water.
Meanwhile, melt butter in a large sauté pan over medium heat.
Add pancetta and cook until crispy and rendered.
Add chopped onion and garlic to the pan, and sauté in the pancetta fat until translucent.
Season with salt and pepper to taste.
Deglaze the pan with chicken stock or white wine, scraping up any browned bits.
Stir in heavy cream and reserved pasta water.
Simmer the sauce gently for about 10 minutes, until slightly thickened.
Stir in Parmesan cheese and fresh herbs during the last 5 minutes of simmering.
Add the drained pasta and broccoli to the sauce, and toss to coat.
Serve topped with extra Parmesan and a sprinkle of Italian parsley.