The Best Slow-Cooked Tomato Sauce

"Great ingredients and a long stay in a low oven are the keys to the best Italian-American Red Sauce. [Photographs: J. Kenji Lopez-Alt] This rich and hearty red sauce tastes like it's been cooked for hours, because it has. The secret to its deep, naturally sweet, complex flavors is to cook the sauce in the oven, allowing the surface to brown while the sauce slowly concentrates. The resultant sauce is great on pasta, with meatballs, on your chicken parm, or scooped right out of the pan with a spoon on its own. Why this recipe works: * Great sauce starts with great ingredients. Use the best whole peeled canned tomatoes you can find, preferably San Marzano D.O.P. tomatoes. * A mixture of butter and olive oil gives the sauce extra richness while mellowing out the stronger flavors. * A whole onion and a carrot added to the sauce while it simmers adds natural sweetness without overwhelming it with extra flavors or being cloying. * Cooking the sauce in the oven not only helps it reduce more evenly (with less stirring required), but it also adds complexity by caramelizing the top surface. * Fish sauce, if you'd like to use it, adds rich, intensely savory flavor (and no, it won't make the sauce taste fishy). * Saving some of the tomatoes for the end and stirring them in gives the sauce a layer of freshness. Note: Use the best tomatoes you can find. D.O.P. San Marzano tomatoes imported from Italy are readily available and a guarantee of quality, though any high quality domestic or imported canned tomato will work. Make sure that the San Marzano tomatoes you look for are labeled "D.O.P.," not just "San Marzano-Style"...."