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1
Preheat the oven to 350 degrees F.
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2
Bring a large pot of salted water to a boil.
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3
Add the spinach and cook for 2 minutes.
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4
Drain in a fine mesh strainer, pressing with a large spoon to release as much water as possible.
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5
Finely chop and set aside.
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6
In a large skillet, melt 1 tablespoon of the butter over medium-high heat.
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7
Add the shallots and garlic and cook, stirring, for 1 minute.
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8
Add the mushrooms, 1/4 teaspoon each of the salt and black pepper, and cook, stirring, until the mushrooms are tender and have given off their liquid, about 5 minutes.
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9
Remove from the heat and let cool.
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10
To make the bechamel sauce, in a large saucepan, melt the remaining 4 tablespoons butter over medium heat.
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11
Add the flour and cook, stirring with a wooden spoon, to make a light roux, about 2 minutes.
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12
Whisking constantly, slowly add the milk and continue to cook, stirring occasionally until thickened, 2 to 3 minutes.
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13
Add the remaining 1/2 teaspoon salt, 1/4 teaspoon black pepper, the nutmeg, and 1 cup of the Parmesan and cook, stirring, until thickened, about 2 minutes.
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14
Remove from the heat.
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15
In a bowl, combine the ricotta, fontina, and mozzarella cheeses.
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16
Fold in 1/4 cup of the bechamel sauce.
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17
Across the bottom of a deep-dish lasagna pan (13 by 9-inches), spoon enough bechamel sauce to cover (about 1/2 cup).
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18
Then add 1/4 of the mushrooms and sprinkle 1/4 of the spinach across.
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19
Arrange a layer of cooked noodles side-by-side across the sauce.
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20
Spread another layer of bechamel over the noodles and top with more spinach, mushrooms, and cheese.
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21
Repeat layering with sauce, noodles, spinach, and cheese 2 more times, ending with noodles on top.
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22
Sprinkle the remaining 1 1/2 cups of Parmesan over the top, cover tightly with aluminum foil, and bake until the noodles are tender and the lasagna is hot and bubbly, about 30 minutes.
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23
Uncover and continue baking until golden brown on top, about 10 minutes.
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24
Let rest for 10 to 15 minutes before serving.
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25
Serve hot.
