Bring a large pot of generously salted water to a boil over high heat.
While the water comes to a boil, in a large skillet over medium-high heat, warm the oil. Add the onions and 1/4 teaspoon salt and stir well to combine. Cook, stirring frequently and adjusting the heat as necessary so the onions don’t burn, for 10 minutes.
Add the sausage to the skillet, using a spoon to crumble the sausage, and stir it into the onions. Continue to cook, stirring often, until the sausage is cooked through and the onions are deeply golden brown, about 25 minutes more.
When the water comes to a boil, add the pasta and cook according to the package instructions.
When the pasta is tender, scoop out 1 cup of the pasta water with a measuring cup. Drain the pasta.
Slowly pour 1/4 cup of the pasta cooking water and the wine over the onions and sausage. Cook, stirring and scraping the brown bits from the bottom of the skillet, for 2 to 3 minutes.
Stir in the cooked pasta. If the sauce seems a touch too thick, add more of the reserved pasta cooking water, a little at a time.
Serve it straight from the skillet or dump the pasta into a large bowl. Grate some Parmesan over the top and, if desired, grind some black pepper over the pasta.