The addition of bay leaves gives this basic tomato sauce a distinctive herbal flavor. Both butter and olive oil are used here, which is unusual. The flavor of bay leaves goes well with olive oil, while the butter makes the sauce mellower.
Fill a pot for the pasta with about 6 quarts of water, place over high heat, and bring to a boil.
Peel the onion and slice thinly crosswise. Put it with the olive oil and butter in a 12-inch skillet. Place over medium-high heat, season lightly with salt, and sauté until the onion turns a rich golden color, 6 to 8 minutes.