Servings: 6 to 8

1 stick salted butter 1 stick salted butter
2 tsp. kosher salt, plus more to taste 2 tsp. kosher salt, plus more to taste
12 lasagna noodles 12 lasagna noodles
3 bunches fresh spinach, trimmed 3 bunches fresh spinach, trimmed
Black pepper, to taste Black pepper, to taste
2 garlic cloves, chopped 2 garlic cloves, chopped
1/4 c. all-purpose flour ¼ c. all-purpose flour
4 c. whole milk 4 c. whole milk
1 c. heavy cream 1 c. heavy cream
1 3/4 c. grated parmesan cheese 1 ¾ c. grated parmesan cheese
1 lb. whole-milk ricotta cheese 1 lb. whole-milk ricotta cheese
2 large egg yolks 2 large egg yolks
1 c. fresh parsley, roughly chopped 1 c. fresh parsley, roughly chopped
4 scallions, chopped 4 scallions, chopped
8 oz. ounces deli-sliced low-moisture mozzarella cheese 8 oz. ounces deli-sliced low-moisture mozzarella cheese

Preheat the oven to 400°.
Use 1 tablespoon butter to grease a 9-by-13-inch flame-proof baking dish.
Bring a large pot of salted water to a boil.
Add the noodles and cook about 3 minutes shy of the package cooking time.
Drain and rinse under cold water.
Melt 2 tablespoons butter in a dutch oven over medium heat.
Add the spinach, season with 1⁄2 teaspoon salt and some pepper; cook, stirring, until wilted, 3 to 4 minutes.
Add half of the garlic and cook 1 to 2 minutes.
Drain and let cool slightly, then wrap in a clean kitchen towel and wring out the liquid.
Wipe the dutch oven clean.
Add the remaining 5 tablespoons butter and melt over medium heat.
Whisk in the flour and cook, whisking, until smooth and thick, about 2 minutes.
Add the remaining garlic and 1 teaspoon salt and cook until sizzling, about 30 seconds.
Slowly stir in the milk and heavy cream. Bring to a simmer, stirring constantly; cook, stirring, until thickened, about 5 minutes.
Whisk in 1 cup parmesan and remove from the heat.
Stir together the ricotta, egg yolks, parsley, scallions, 1⁄2 cup parmesan, 1⁄2 teaspoon salt and some pepper in a medium bowl.
Spread 1 cup of the sauce in the baking dish.
Arrange 4 noodles lengthwise in the dish.
Spread with another 11⁄2 cups sauce.
Layer half of the mozzarella over the sauce, then spread with half of the ricotta mixture and half of the spinach.
Repeat the layering (noodles, sauce, mozzarella, ricotta and spinach).
Top with the remaining 4 noodles and spread with the remaining sauce (about 1 cup).
Sprinkle with the remaining 1⁄4 cup parmesan.
Cover with foil, tenting it so it doesn’t touch the lasagna.
Place on a baking sheet and bake until the edges begin to bubble, about 20 minutes.
Uncover and bake until golden brown on top, 30 to 35 minutes.
Switch the oven to broil and broil 1 minute to brown the top.
Let sit 15 minutes before serving.