Slow Cooker

1. Heat a large skillet over medium-high heat. Add the ground sausage and onion. Cook until the sausage is browned and no longer pink, crumbling it with a spatula as it cooks. Add the garlic and cook for 1 additional minute. Drain the excess grease and transfer the sausage mixture to the slow cooker.
2. Add the crushed tomatoes, tomato sauce, beef broth, Italian seasoning, fennel seeds, salt, pepper, and red pepper flakes (if using). Stir to mix well.
3. Cover and cook on HIGH for 3 to 4 hours or on LOW for 6 to 8 hours.
4. If the slow cooker is set to LOW, turn it to HIGH. Stir in the broken lasagna noodles during the final 20 to 30 minutes of cooking. Cover and cook until the noodles are tender, stirring once or twice to prevent them from sticking together.
5. While the noodles cook, combine the ricotta, mozzarella, and Parmesan in a medium-size bowl.
6. When the noodles are tender, stir the soup and add more beef broth if you prefer a thinner consistency. Taste and adjust the seasonings as needed.
7. Ladle the hot soup into bowls and top each serving with a generous spoonful of the cheese mixture.

Instant Pot

1. Set the Instant Pot to sauté. Add the ground sausage and onion. Cook until the sausage is browned and no longer pink, crumbling it as it cooks. Drain any excess grease.
2. Add the garlic and cook for approximately 1 minute, stirring frequently. Turn off the sauté function.
3. Pour in the beef broth. Use a wooden spoon to scrape all the browned bits from the bottom of the pot to help prevent a burn notice.
4. Stir the Italian seasoning, fennel seeds, salt, pepper, and red pepper flakes into the broth.
5. Add the broken lasagna noodles and gently press them into the liquid. Pour the tomato sauce and crushed tomatoes evenly over the top. Do not stir.
6. Close and seal the lid. Cook on HIGH pressure for 4 minutes.
7. When the cooking time is complete, carefully quick release the pressure.
8. Open the lid and stir the soup well, separating any noodles that have stuck together. Let it sit for 5 to 10 minutes; the broth will thicken slightly as it rests. Add more beef broth if you prefer a thinner soup.
9. Combine the ricotta, mozzarella, and Parmesan in a separate bowl. Ladle the soup into bowls and top each serving with a generous spoonful of the cheese mixture.