In a large skillet over medium-high heat sauté ground beef and onion until it's cooked through. Drain off any excess grease.: Right away you should notice the sound of the meat sizzling and the onion turning translucent, releasing a sweet aroma that softens the raw edge. The sizzling indicates the skillet is hot enough to develop browned bits, those tiny crusty fragments that carry savory flavor into the chili, so listen for a steady sizzle rather than a gentle simmer. As the ground beef browns, break it apart with your spoon so it caramelizes evenly; the visual cue is when most pieces are richly browned rather than gray. For the onion , watch for edges to go glossy and soft, which means the sugars have started to release and will sweeten the pot. A common mistake here is overcrowding the pan which causes the meat to steam and fail to brown properly, yielding a flatter taste. Drain off excess grease after browning to prevent an overly oily texture, but leave some fond if you can, as it dissolves into the base and deepens flavor.
Transfer ground beef and onions to a 6 quart slow cooker. Add the rest of ingredients and stir to combine.: As you pour off fat you should see clearer liquid separate from the solids, and the smell will shift from greasy to concentrated meatiness. Removing excess fat helps the final chili feel balanced rather than heavy, and keeps the surface from being slick. Use a heatproof container or tilt the skillet carefully; the visual is a thinner layer of oil collecting at the edge. Avoid removing all cooking juices, because those browned bits cling to the pan and hold flavor. A mistake to avoid is tossing all the drippings as if they are worthless, since a little retained fond noticeably improves complexity.
Cook on high 3-4 hours or low 6-8 hours.: When you scrape the skillet into the slow cooker, you should see a mix of browned meat and softened onion, and perhaps a few browned flecks left behind that you can deglaze if you like. This transfer marks the point where the pot takes over, and that initial aroma will begin to mingle with tomato notes once other ingredients are added. Ensure the slow cooker is large enough so ingredients have room to simmer without spattering, and spread the meat evenly to allow even heat penetration. A common oversight is dumping everything into an undersized cooker which can cause uneven cooking and longer times.
Top with sour cream and cheese if desired.: After adding canned tomatoes , tomato sauce , chili beans , water, and spices, you should see a colorful mix from red to speckled herbs. Stirring incorporates spices like chili powder , cumin , and oregano so they disperse and infuse the liquid; you want a homogenous base where the spices are suspended, not sitting in clumps. The aroma will shift immediately as the acidic tomato brightens the pot and the spices warm up. Stir until you no longer see dry pockets of seasoning. A frequent error is under-stirring, which leaves uneven pockets of spice that taste sharp rather than integrated.
Cook on high 3-4 hours or low 6-8 hours: The slow cooker will transform these ingredients into a cohesive chili as heat and time coax flavors together. On high, you should see gentle bubbling and steam from the lid after an hour or two, while on low the surface will simmer with small, occasional bubbles; either approach breaks down tomatoes and melds spices, but low and slow offers more nuanced depth. Fragrant steam should smell warm and savory rather than sharp, and the texture should progress from soupy to a thick, spoonable stew. One common slip is lifting the lid frequently to check, which releases heat and extends cooking time, so resist peeking unless necessary. If the chili is thinner than desired near the end, remove the lid and cook uncovered briefly to reduce.
Top with sour cream and cheese if desired: When serving, the cool tang of sour cream and the melty richness of shredded cheese make a wonderful contrast to the warm, spiced chili. You should notice a creamy ribbon when the sour cream sinks in, and a glossy melt when cheese meets hot chili. These toppings also moderate heat and add texture contrast, making each bite more interesting. A mistake is adding dairy too early into hot chili, which can separate or curdle; save them for the table so guests can customize their bowls.