Make roux with butter, garlic, flour, and salt. When bubbly remove from heat. Stir in milk and broth. Heat this until boiling. Continue to cook, while stirring constantly, for one minute or until thickened. Add onion, basil, and mozzarella. Cook over very low heat until cheese is melted.
Spread 1 1/2 cups of this mixture on bottom of 9X13 inch pan.
Top with 3 or 4 UNcooked lasagne noodles. Spread cottage cheese over this. Repeat with another quarter of the sauce and 3 or 4 more noodles. Top this with crab and shrimp and another quarter of the sauce. Add 3 or 4 more noodles and top with remaining sauce.