Cook linguine according to package directions until al dente.

In a saucepan over medium heat, bring chicken broth to a boil.

Add chopped onion and minced garlic to the boiling broth.

Reduce heat to a simmer and cook uncovered for 5 minutes, until onions soften.

Stir in thawed and drained spinach, cook for 2 more minutes.

Add milk, cream cheese, salt, and pepper.

Stir until cream cheese is melted and sauce is smooth.

Drain the cooked linguine.

Place the drained linguine in a serving bowl.

Pour the sauce over the linguine and toss to coat evenly.

Sprinkle grated parmesan and mozzarella cheeses over the pasta.

Toss again to coat with cheese.