This is one of the first things I think of when I think of "comfort food." It was the first meal fed to me when I was a student in Italy ten years ago. It's simplicity in action, calling for only a handful of ingredients. But the quality of those ingredients really matters more than the quantity--I'd recommend using San Marzano tomatoes (or something similar) and good olive oil. And when I say mince the onion, I mean really mince. You want them to practically dissolve into the oil and butter by the time you're ready to add the tomatoes. This recipe is for 4, but the quantity of ingredients can be easily halved (or, if you're feeding a crowd, doubled or tripled). —Chris Hagan
Combine the oil, butter, and minced onion in a large saucepan or skillet. (Don't melt the butter first--you want everything to cook together.) Set over a VERY low flame, cover, and cook 35-40 minutes (possibly longer; it's question of color and texture), stirring occasionally. Basically you want them to be very, very soft--not much crunch--and deeply, deeply golden, but not browned or burnt, hence the low heat.
Stir in the tomatoes, cover, and simmer another 20-30 minutes, stirring occasionally. Uncover and stir in the cream. Season with salt and pepper to taste.
Meanwhile, bring a large pot of well-salted water to a boil, add the pasta, and cook until al dente. Add the pasta to the tomato sauce along with the swiss cheese, toss to combine, and serve garnished with chopped parsley or chives (if using).