Heat a large skillet (15″ or bigger) over medium high heat.

While the pan heats, prepare the onions by cutting off both ends and peeling away the tough outer layer. Cut each onion in half and slice into 1/4″ half moon slices.

When the pan is hot but not smoking, add 2 Tablespoons olive oil and the sliced Italian sausage. Cook for 1-2 minutes to brown each side before removing the sausage from the pan. Set it aside until the end of the cooking time.

Add the remaining 2 Tablespoons of olive oil along with the sliced onions. Sprinkle with a small amount of sea salt (1/2 Teaspoon) and cook onions stirring every few minutes for 10-15 minutes or until soft and browned.

While the onions cook, prepare the rest of the ingredients. For the broccoli rabe, stack 4-5 stalks together at a time and roughly slice into 1/2″ pieces. Cut the mushrooms into 1/4″ slices.

Bring a large pot of water to boil (3-4 quarts of water and 1 Tablespoon sea salt). When the onions are done cooking, add the pasta to the pot of boiling water and cook according to package directions, it’s usually 8-10 minutes which is just enough time to finish the rest of the recipe.

While the pasta cooks, add the rosemary, broccoli rabe, and mushrooms to the skillet with the caramelized onions. Lower the heat to medium and cook stirring every few minutes until the broccoli rabe is just tender, 6-8 minutes.

If at anytime the veggies start to stick, add a small amount of the pasta cooking water to the pan.

When the pasta is done (al dente with a bit of a bite to it) measure out 1 cup of pasta water before draining the pasta. Turn the heat back up to medium high for the skillet, and add the drained pasta, Italian sausage, and veggies, along with the pasta water and half of the parmesan if you’re using it.

Adjust the seasoning by adding sea salt and freshly ground black pepper to taste.

Serve immediately with a sprinkling of the remaining parmesan and more freshly ground pepper to taste.