Heat a very large pot or Dutch oven over medium-high heat and brown the ground beef with the diced onion, stirring often, until the beef is cooked through; drain excess fat. Keep the heat at medium-high so the beef browns rather than steams.

Add the drained black beans, drained kidney beans, drained pinto beans, drained corn, Rotel tomatoes, and diced tomatoes to the pot along with the taco seasoning, ranch dressing mix, and Hidden Valley original Ranch; stir to combine. Make sure all canned ingredients are evenly distributed and coated in the seasoning.

Pour in the beef broth and bring the mixture to a boil, stirring once or twice to prevent sticking at the bottom. Look for steady bubbling across the surface before reducing heat.

Reduce heat to maintain a gentle simmer and cook for 15-20 minutes, stirring occasionally, until the soup thickens slightly. Keep it at a low, active simmer rather than a hard boil for best texture.

Season with salt and pepper to taste, then stir well and let it sit for 2 minutes off the heat. Taste again after it rests briefly so the flavors settle.

Serve hot with a very generous topping of shredded cheddar, sour cream, lots of tortilla chips, and green onions. Add toppings right before eating so the chips keep their crunch.