Start by slicing two medium brown or yellow onions into thin strips. Heat a large skillet over medium-low heat and add 2 tablespoons of unsalted butter. Stir the onions into the melted butter, allowing them to cook slowly for about 20-25 minutes until they're golden brown and softened. Stir occasionally.

While the onions are caramelizing, bring a large pot of salted water to a rolling boil. Add your choice of pici or long noodles and cook until al dente, approximately 8-10 minutes. Reserve about 1 cup of the starchy pasta water before draining the pasta.

Once the pasta is cooked and drained, return it to the skillet with the caramelized onions. Add another tablespoon of butter and a generous amount of freshly grated Parmesan cheese. Sprinkle in freshly cracked black pepper, adjusting to your taste, and toss over low heat for about 2-3 minutes.

If the sauce appears too thick, gradually incorporate more reserved pasta water, stirring continuously to ensure the cheese melts smoothly and clings to the pasta.

Plate the dish in warm bowls, drizzling with balsamic glaze if desired, and serve immediately.