Preheat oven to 375 degrees F (190C). Grease a 9x13 baking dish with butter or oil and set aside.
Bring a large pot of salted water to a boil over high heat. Add the lasagna noodles carefully and par cook for 4 minutes, stirring them occasionally to prevent the sheets from sticking together. After 4 minutes, use tongs to remove the noodles and spread them out on parchment or wax paper to cool while you make the Alfredo sauce and filling.
In a large skillet, melt butter over medium heat. Add garlic and cook for 1 minute or until fragrant. Add heavy cream and broth and bring to a simmer on medium high heat, cooking for about 5 to 7 minutes. Stir consistently as it bubbles and thickens, scraping down the sides of the pan.
Add the Boursin cheese to the cream sauce and mix until fully melted and incorporated into the sauce, about 2-3 minutes. Stir in 1 teaspoon of kosher salt and ½ teaspoon of pepper. Remove from the heat.
In a medium bowl, add the chicken, spinach and ½ cup of the Alfredo sauce and toss with tongs until fully mixed. Season to taste and set aside. To a small mixing bowl, add the ricotta, ½ teaspoon of salt and ¼ teaspoon of pepper and mix well.
Assemble the lasagna - Spread 1/3 cup of alfredo sauce evenly across the bottom of the baking dish with the back of a spoon. Layer 3 lasagna noodles across the baking dish then spread 1/3 of the ricotta across the noodles with the back of a spoon. Top with 1/3 of the chicken mixture and sprinkle 1/2 cup shredded mozzarella. Repeat this layering 2 more times, then add one more layer of lasagna noodles. Spoon the remaining Alfredo sauce on top and then sprinkle 1/2 cup of shredded mozzarella over it.
Cover the baking dish with aluminum foil and bake at 375F on the middle rack for 20 minutes. After 20 minutes, remove the foil and bake, uncovered, for another 10 minutes. Remove from the oven and let the lasagna cool for 10 minutes. Garnish with fresh parsley, slice and serve.
Notes
*Lasagna noodles - Boil a few extra just in case some break or rip if you care about them looking pretty! I used Barilla in recipe testing. Gluten free noodles can be subbed.
Use whole milk ricotta brands like Calabro, BelGiosio, or Liuzzi for best results. These are super creamy and not grainy.
Use leftover chicken or a plain rotisserie chicken. I like to get mine from Sprouts or Whole Foods with just salt and pepper.
Spinach can be subbed with chopped kale for low histamine. This recipe fits HYH as is.