Start by bringing a large pot of water to boil to cook the pasta. Many home cooks, including myself, underestimate how long it takes to (1) bring the water to boil and (2) cook the pasta. We end up with a finished sauce waiting for the pasta to cook.
Get the water boiling before you need to throw in the pasta. And don't forget to season the water with a little salt.
Add the pasta and bring the water back to a boil and cook until al dente (tender yet firm).
While the pasta is cooking, melt the 2 tablespoons of butter in a large fry pan (sauté pan) big enough to hold both the sauce and the pasta over medium-high heat.
Add the cipollini onions and sage and cook until the onions are lightly brown. This should take about 4 minutes.
Season the onions and sage with salt and pepper and add the minced chicken livers. These cook quickly, about a minute or two.
Add a ladle full of the pasta water using it to deglaze, scraping the bottom of the pan to loosen up anything stuck to it.
When it's time to drain the pasta and add it to the sauce, be sure to reserve a cup of the pasta water in case you need it when making the sauce. Pasta water, full of starch from the pasta, is a great way to help the sauce stick to the pasta.
Add the pasta to the saucepan and toss with the Parmesan cheese, some of the reserved pasta water and additional butter. Judgment time. If you think you need more sauce or it is not creamy enough, add a little more of the pasta water.
You can also add more butter but don't overdo it. I think restaurants are using way too much butter in their sauces, but that is another topic for discussion.
Serve in a large bowl family style or divide among individual bowls and serve with the extra Parmesan cheese as a garnish. It is also a great idea to warm the bowls before adding the pasta to keep everything warm.