2 1/2 tablespoons olive oil
1 onion, chopped in a medium dice
1 teaspoon kosher salt, divided
3 sprigs thyme, finely chopped
1/2 teaspoon red chili flakes
3 cups fresh baby spinach
3 cloves garlic, minced
3 cups chicken breast, cooked
3 cups chicken stock
1 1/2 cups milk
1/2 cup all purpose flour
1/4 teaspoon ground nutmeg
1/2 cup Parmesan cheese, grated
12 lasagna noodles
1 1/4 cups mozzarella cheese, shredded
Preheat oven to 375 degrees Fahrenheit and grease a 9" x 13" casserole dish.
Heat oil in a large skillet set over medium-high heat. When oil is hot, add onion, 1/2 teaspoon salt, thyme, and red chili flakes. Saute for about 3 minutes.
Add spinach, in batches if necessary, and cook for about 1 minute until it just begins to wilt.
Add garlic and cook for another 30 seconds.
Remove pan from heat and stir in cooked chicken.
Heat chicken stock over medium-high heat until it boils. Lower heat to a simmer.
Combine milk, flour, and nutmeg. Whisk until smooth.
Gradually add the milk mixture to the hot stock on the stove, whisking as you do to prevent lumps from forming.
Stir in remaining 1/2 teaspoon of salt, and simmer the milk and stock mixture for 5 minutes or until thickened slightly.
Remove saucepan from heat and stir in Parmesan cheese.
Pour 1 cup of the sauce into the bottom of prepared casserole dish.
Spread 3 or 4 lasagna noodles over sauce, then top with 1 1/2 cups chicken mixture.
Add another 3/4 cup of sauce and 1/4 cup of the mozzarella cheese.
Repeat layers until all ingredients are used, ending with lasagna noodles topped with 1/4 cup of sauce and the remaining 3/4 cup of mozzarella.
Cover the lasagna with foil and place in oven for 40 minutes.
Remove foil and bake for another 15 to 20 minutes, until cheese is browned and lasagna is heated throughout.
