In a large sauté pan, heat the olive oil and cook the bacon or pancetta over medium heat until it begins to render its fat and brown around the edges. Add the onion and garlic and cook gently until the onion is soft and beginning to turn golden. Add the chili flakes, if using, then pour in the Marsala. Let it bubble for a minute or two, scraping up anything browned on the bottom of the pan.

Meanwhile, cook the pasta in well-salted water until just al dente. Before draining, reserve about a half a cup of the pasta cooking water.

Add the drained pasta directly to the pan and toss everything together, adding a splash of pasta water as needed. Keep tossing until the rendered bacon fat, Marsala and pasta water come together and lightly coat the pasta.

Remove from the heat, add the cheese and toss again. Add another splash of pasta water if it seems dry, then serve with more cheese at the table.