Collect all the necessary ingredients before you begin. This ensures you have everything on hand, making the cooking process smoother and more efficient. Preparing in advance helps you stay organized and ensures you don't miss any crucial components while cooking.
In a large nonstick skillet, combine the ground beef, onion, garlic, ½ teaspoon salt, and ½ teaspoon black pepper. Cook over medium-high heat, stirring occasionally, until the beef is browned and cooked through, and the onions are softened, about 8 minutes. Once cooked, transfer the mixture to a 6-quart slow cooker. This step allows the flavors to meld together before continuing the cooking process in the slow cooker.
Add the beef broth, marinara sauce, diced tomatoes, tomato paste, crushed red pepper, 1 teaspoon salt, and ¼ teaspoon black pepper to the slow cooker. Stir everything together until well combined. This ensures that the flavors blend evenly, creating a rich and flavorful base for the soup.
Cover the slow cooker and cook on LOW for 3 ½ to 4 hours, or on HIGH for 2 hours, until the soup has thickened slightly. This slow cooking process allows the flavors to fully develop and the broth to reduce, resulting in a rich, hearty soup with a satisfying texture.
Stir the broken lasagna noodles into the crockpot, ensuring the pieces are fully submerged in the liquid. Cover the slow cooker and cook on HIGH for about 30 minutes, or until the noodles are al dente. This step allows the noodles to absorb the flavors of the broth and become tender without overcooking.
Add the spinach to the crockpot during the last 5 minutes of cooking. Stir it in gently, allowing it to wilt and blend into the soup, adding a fresh, vibrant flavor and a boost of nutrition to the dish.
Serve the soup with a generous dollop of ricotta cheese and a sprinkle of Parmesan on top. Garnish with a pinch of crushed red pepper for an extra kick of heat and a burst of flavor. This finishing touch adds richness and a subtle spice, elevating the dish’s taste and presentation.