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1
In a medium saucepan, melt 3 tablespoons butter over low heat.
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2
Stir in the flour and cook for 2 minutes.
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3
Slowly whisk in the hot milk, then the smashed garlic clove and 3/4 teaspoon salt.
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4
Bring the garlic sauce to a boil and cook, whisking, until thickened, about 5 minutes.
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5
Set aside.
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6
In a large pot of boiling salted water, cook the lasagna noodles for 8 minutes.
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7
Drain and transfer to a bowl of cold water.
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8
Position a rack in the center of the oven and preheat to 375.
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9
In a large skillet, melt the remaining 2 tablespoons butter over low heat.
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10
Add the onions and chopped garlic and cook until softened, about 5 minutes.
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11
Stir in the mushrooms and cook until softened, about 7 minutes.
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12
Using a food processor, puree the basil leaves with the cream.
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13
Set aside 1/2 cup basil cream.
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14
Stir the remaining basil cream and 1/2 cup parmesan into the mushroom mixture; season with salt and pepper.
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15
Grease a 9-by-13-inch baking dish and spread 1 cup reserved garlic sauce on the bottom.
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16
Drain the lasagna noodles and lay 3 in the baking dish.
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17
Top with half of the mushroom mixture, a layer of noodles, then the remaining mushroom mixture and noodles.
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18
Combine the remaining garlic sauce and basil cream; spoon on top.
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19
Sprinkle with the remaining 3/4 cup parmesan.
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20
Bake until golden, 40 to 45 minutes.
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21
Let stand for 15 minutes.
