Boil lasagna sheets according to package instructions until al dente. Drain and separate lasagna sheets on a baking sheet or parchment paper. Set aside for later.
In a large skillet over medium heat, add ground sausage, ground beef and chopped onion. Cook, stirring occasionally until sausage is cooked through and onions are tender, about 4-5 minutes. Add minced garlic in the last minute. Next, add pasta sauce, broth and Italian seasoning. Stir to combine and allow it to simmer over low heat for about 10-15 minutes. Remove from heat when done and let cool slightly.
Preheat oven to 350 degrees.
In a medium bowl, mix together ricotta cheese, cottage cheese, chopped spinach,1 cup mozzarella cheese, ¼ cup parmesan cheese, egg, salt (if using) and pepper.
Spread about ¼ of the meat sauce to cover the bottom of your baking dish.
Make the lasagna roll ups by laying out each sheet of lasagna on a flat surface and spreading about 2 tablespoons of the ricotta mixture onto each sheet. Top the ricotta mixture with about 3-4 tablespoons of meat sauce. Roll lasagna sheet up and place in baking dish with the seam facing down. Repeat with all 12 rolls.
Add any remaining meat sauce on top of the rolls, spreading it over the edges of the rolls as well to prevent them from drying out. Sprinkle with remaining mozzarella and parmesan cheese.
Cover dish with foil and bake for 35 minutes. Carefully remove foil and let cook another 5 minutes.
Remove lasagna roll ups from oven and let cool for a few minutes before serving. Garnish with finely chopped parsley, if desired. Enjoy!