Brown the beef: Heat a large, deep skillet or Dutch oven over medium-high heat. Add the ground beef (2 pounds) and cook, breaking it into bite-sized pieces with a wooden spoon, until it's no longer pink and nicely browned, about 8–10 minutes. If there's an excessive amount of grease, carefully spoon off enough to leave about 2 tablespoons in the pan.
Cook the onion: Add the diced onion (1) and cook until softened, about 4–5 minutes. Stir in the garlic (4 cloves) and cook for 30 seconds, just until fragrant.
Build the flavor: Stir in the tomato paste (3 tablespoons) and cook for 2 minutes, stirring constantly, until it darkens slightly. Add the Worcestershire sauce (1 1/2 tablespoon), soy sauce (1 teaspoon), Better Than Bouillon (2 teaspoon), smoked paprika (2 teaspoons), garlic powder (1 teaspoon), onion powder (1 teaspoon), dry mustard (1 teaspoon), fine salt (1 teaspoon), and black pepper (1 teaspoon). Cook for 1 minute, stirring constantly, until fragrant.
Add the liquids: Pour in the beef broth (3 cups) and whole milk (2 cups), scraping the bottom of the skillet to loosen any browned bits. Bring the mixture to a gentle boil.
Cook the pasta: Stir in the elbow macaroni (12 ounces). Reduce the heat to low, cover, and maintain a gentle simmer for 10–12 minutes, stirring occasionally, until the pasta is just tender and most of the liquid has been absorbed. If the pasta begins to look dry before it's fully cooked, stir in a splash of beef broth as needed.
Finish the sauce: Remove the skillet from the heat. Gradually stir in the shredded cheddar (2 cups) and Monterey Jack cheeses (2 cups), allowing each addition to melt completely before adding more. Stir in the butter (2 tablespoons) until melted, then add the whole milk and stir until the sauce is smooth, creamy, and silky. Let the Hamburger Helper rest for 2–3 minutes before serving so the sauce can thicken slightly and cling to the pasta. Serve: Taste and adjust the seasoning if needed. Garnish with chopped fresh parsley, if desired, and serve hot.