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1
Preheat the oven to 400F.
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2
On a baking sheet, toss the sweet potatoes with the oil, 1/2 teaspoon salt and 1/4 teaspoon pepper.
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3
Roast the squash in the oven until tender, about 30 minutes.
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4
While the sweet potatoes roast, make the sauce: In a large heavy pot, heat the butter over medium high heat until hot.
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5
Stir in the onion, garlic, 1 teaspoon salt and 3/4 tea-spoon pepper, and cook, stirring, until golden, about 8 minutes.
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6
Stir in the flour and cook, stirring, 1 minute.
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7
Whisk in the milk and bring to a boil, whisking.
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8
Boil 5 minutes, then remove from the heat.
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9
Season the sauce with salt and pepper to taste.
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10
In a 3-to 3 1/2-quart lasagna dish spread 1 cup of the sauce over the bottom.
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11
Place 3 lasagna noodles evenly over the sauce, leaving even space between the noodles.
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12
Top the noodle layer evenly with a layer of sauce, then place another 3 noodles on top.
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13
Spread an even layer of sauce over the noodles, then spread half the sweet potatoes over the sauce.
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14
Top with another layer of 3 noodles, then sauce and the remaining sweet potatoes, then the remaining 3 noodles and sauce.
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15
Top with the cheddar cheese.
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16
Cover the lasagna dish with aluminum foil and bake until the filling is bubbling, about 45 minutes.
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17
Uncover the dish and continue to bake until the cheese is golden in places, about 30 minutes more.
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18
Let the lasagna stand 10 minutes before serving.
