Spinach Mushroom Lasagna (Print Version)

# Ingredients:

→ For the Spinach Mushroom Filling

01 - 4 tbsp unsalted butter
02 - ½ cup white onion or shallot, finely diced
03 - 6 garlic cloves, minced
04 - 1 tsp kosher salt plus more to taste
05 - Black pepper to taste
06 - 8 oz white mushrooms, finely chopped
07 - 1 tbsp Italian seasoning
08 - 16 oz frozen spinach, thawed and drained

→ For the Ricotta Mixture

09 - 30 oz whole milk ricotta
10 - ½ cup Parmigiano Reggiano, finely grated
11 - 2 large eggs
12 - ¼ cup fresh parsley, chopped
13 - 8 oz low-moisture mozzarella cheese, shredded and divided

→ For the White Sauce

14 - 5 tbsp unsalted butter
15 - 5 tbsp all-purpose flour
16 - 5 cups whole milk, at room temperature
17 - ½ cup Parmigiano Reggiano, finely grated
18 - 1 tsp kosher salt, or more to taste
19 - Black pepper to taste
20 - ½ tsp ground nutmeg

→ For Assembly

21 - 1 lb lasagna noodles (about 20 noodles)
22 - Olive oil for drizzling
23 - Non-stick cooking spray

# Instructions:

01 - Thaw your frozen spinach completely and squeeze out as much water as you can. The best way to do this is to put the spinach in a metal steamer basket and close the sides to squeeze, or use cheesecloth. This works way better than paper towels and gets rid of more moisture.
02 - Cook the lasagna noodles until they're al dente according to the package directions. Drain them, rinse under cold water to stop the cooking, and lay them flat on sheets of parchment paper. Drizzle a little olive oil over them so they don't stick together. This makes them easier to work with when you're assembling later.
03 - Melt the butter in a large nonstick skillet over medium-high heat. Add the onions, salt, and pepper and cook for 2 to 3 minutes, stirring every now and then. Toss in the garlic and cook for another minute. Add the chopped mushrooms and Italian seasoning. Keep cooking until the mushrooms shrink down and all the liquid evaporates - this takes about 7 to 10 minutes. Stir occasionally.
04 - Take the skillet off the heat and stir in your drained spinach. Add a little more salt and pepper to taste. Set this aside to cool down.
05 - In a large bowl, mix together the ricotta, Parmesan cheese, half of the shredded mozzarella, eggs, and parsley. Once your spinach and mushroom mixture has cooled, add it to the ricotta mixture and combine everything together.
06 - In a large heavy-bottomed saucepan, melt the butter over medium heat. Add the flour and whisk to make a roux - cook for about a minute. Slowly pour in the milk a little at a time, whisking constantly between each addition. Keep whisking as you add all the milk. Continue whisking over medium heat until the mixture comes to a boil and starts to thicken. Take it off the heat and stir in the Parmesan cheese, nutmeg, salt, and pepper.
07 - Turn your oven to 375 degrees. Pour about half a cup of white sauce (or enough to coat the bottom) into a 9 by 13 inch oven-safe pan.
08 - Add a layer of lasagna noodles on top of the sauce, tearing them as needed to fit the pan. Dollop about a third of the spinach-mushroom-ricotta mixture over the noodles and spread it in an even layer. Drizzle with half a cup of white sauce. Add another layer of noodles and repeat this process two more times.
09 - Put one final layer of noodles on top, pour over the last of the white sauce, and sprinkle the remaining mozzarella cheese over everything. Spray one side of a piece of aluminum foil with nonstick spray and cover the lasagna with the greased side facing down.
10 - Bake covered with foil for 30 minutes. Take off the foil and bake for another 10 minutes until the top is browned and bubbly. You can even broil it for a few minutes at the end for extra browning - just watch it closely so it doesn't burn.
11 - Let the lasagna cool for at least 15 minutes before cutting into it. This helps it set up so the slices hold together. Then dig in and enjoy your creamy, gooey lasagna.

# Notes:

01 - Really squeeze out all the water from the spinach or your lasagna will be watery.
02 - Using room temperature milk for the white sauce helps it incorporate smoothly and prevents lumps.
03 - Drizzling the cooked noodles with olive oil prevents them from sticking together while you work.
04 - Let the mushroom mixture cool before adding to the ricotta or the heat will scramble the eggs.
05 - The 15-minute cooling time is important - it lets the lasagna firm up so it doesn't fall apart when you cut it.
06 - This makes a huge pan and feeds a crowd. Leftovers keep in the fridge for up to 4 days.
07 - You can assemble this completely ahead of time and refrigerate for up to 24 hours before baking. Just add 10 extra minutes to the covered baking time.

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