Preheat oven to 375°F (190°C). Cook lasagna noodles according to package directions until al dente. Drain and set aside.
In a large skillet over medium-high heat, cook ground beef and turkey until browned, about 8-10 minutes. Add diced onion and cook until softened, 3-4 minutes.
Add minced garlic and cook for 1 minute until fragrant. Stir in tomato paste and cook for 2 minutes.
Add marinara sauce, beef broth, Italian seasoning, salt, and pepper. Simmer for 10-15 minutes until sauce thickens slightly. Remove from heat.
In a mixing bowl, combine ricotta cheese, egg, 1/2 cup Parmesan cheese, chopped parsley, and salt. Mix until smooth and well combined.
Spread 1 cup of meat sauce in the bottom of a greased 9x13-inch baking dish.
Layer 4 lasagna noodles over the sauce, overlapping slightly. Spread half of the ricotta mixture over noodles, then sprinkle with 1/3 of the mozzarella cheese.
Add half of the remaining meat sauce, then another layer of 4 noodles. Repeat with remaining ricotta mixture and another 1/3 of mozzarella.
Top with final 4 noodles, remaining meat sauce, remaining mozzarella, and 1/4 cup Parmesan cheese.
Cover tightly with aluminum foil and bake for 45 minutes. Remove foil and bake an additional 15 minutes until cheese is golden and bubbly.
Let lasagna rest for 10-15 minutes before cutting to allow layers to set. Cut into squares and serve hot.
Notes
MAKE-AHEAD:
Assemble lasagna completely, cover tightly, and refrigerate up to 24 hours or freeze up to 3 months. Add 15-20 minutes to baking time if cooking from cold.LAYERING TIPS:
Spread each layer evenly to the edges for clean, even slices. Don't overfill layers as this can cause bubbling over during baking.STORAGE:
Refrigerate leftovers up to 4 days. Individual portions reheat well in microwave for 2-3 minutes or oven at 350°F for 20 minutes.TROUBLESHOOTING:
If top browns too quickly, tent with foil. If lasagna seems watery, ensure meat sauce was simmered long enough to reduce excess liquid.