Heat a large skillet over medium-high heat. Add the ground beef and diced onion; sauté for 6 to 8 minutes, breaking meat into small crumbles, until browned and cooked through. Add minced garlic in the final 60 seconds. Drain any excess fat.

Transfer the seasoned beef and onion mixture into the ceramic basin of a 6-quart or larger slow cooker (crockpot).

Add the crushed San Marzano tomatoes, marinara sauce, beef broth, tomato paste, Italian seasoning, crushed red pepper flakes, salt, and black pepper. Stir thoroughly to combine.

Cover with lid and cook on LOW for 4 to 6 hours (or on HIGH for 2.5 to 3 hours), allowing the tomato and beef aromatics to deepen into a rich, robust broth.

Approximately 30 minutes before serving, break the uncooked lasagna noodle sheets into rough 1.5-inch pieces and stir them directly into the hot bubbling soup.

Cover and cook on HIGH for 25 to 30 minutes, stirring occasionally, until the wavy noodles are perfectly al dente and tender.

In a small bowl, whisk together the whole-milk ricotta, half of the grated parmesan, and a pinch of black pepper and Italian herbs until creamy.

Ladle the hot lasagna soup and curly noodles into wide ceramic bowls.

Immediately top each steaming bowl with a handful of shredded mozzarella (it will melt into gorgeous gooey ribbons), a generous dollop of the seasoned ricotta mixture, and a shower of fresh basil chiffonade.

Serve piping hot alongside crisp toasted garlic bread and a fresh garden salad.