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1
Preheat the oven to 350F (180C).
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2
Bring a large pot of salted water to a boil.
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3
Stir in the spinach and cook for 1 to 2 minutes.
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4
Drain in a fine mesh strainer, pressing with a large back of the spoon to release as much moisture 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 or heat 1 tablespoon of the vegetable oil over medium-high heat.
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7
Stir in the shallots and garlic and cook, stirring, for 2 minutes.
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8
Stir in the mushrooms, season with salt and black pepper, and cook, stirring, until the mushrooms are tender and most of the liquid has evaporated, 4 to 6 minutes.
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9
Remove from the heat and allow to cool.
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10
To make the bechamel sauce, in a large saucepan, melt the remaining 3 tablespoons butter or heat vegetable oil over medium heat.
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11
Mix in the flour and cook, stirring with a wooden spoon, to make a light roux, 3 minutes.
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12
Whisking frequently, gradually pour in the milk and continue cooking, stirring often until thickened, about 3 minutes.
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13
Add extra salt and black pepper to taste, 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 large bowl, mix together 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 1/2 cup of bechamel sauce to cover.
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18
Then evenly place 1/4 of the mushrooms and 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 evenly 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
Top with the remaining 1 1/2 cups of Parmesan evenly, cover tightly with foil papper, and bake until the noodles are tender and the lasagna is hot and bubbly, 30 to 35 minutes.
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23
Uncover and continue baking until golden brown on top, 10 to 15 minutes.
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24
Allow to rest for about 15 minutes.
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25
Serve hot.
