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1
Preheat the oven to 375F.
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2
In a large heavy pot, heat the oil over medium high heat until hot.
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3
Stir in the onion, garlic, 1 teaspoon salt and 3/4 teaspoon pepper, and cook, stirring, until golden, about 8 minutes.
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4
Stir in the flour and cook, stirring, 1 minute.
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5
Whisk in the milk and bring to a boil, whisking.
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6
Boil 5 minutes, then remove from the heat and stir in the mozzarella and asiago cheese until they are melted.
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7
Season the cheese sauce with salt and pepper to taste.
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8
In a 3-to 3 1/2-quart lasagna dish spread 1 cup of the cheese sauce over the bottom.
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9
Place 3 lasagna noodles evenly over the sauce, leaving even space between the noodles.
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10
Top the noodle layer evenly with a layer of cheese sauce, then place another 3 noodles on top.
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11
Spread an even layer of cheese sauce over the noodles, then dollop half the ricotta.
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12
Top with another layer of 3 noodles, then sauce, then the remaining 3 noodles and sauce.
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13
Dollop with the remaining ricotta and sprinkle with the cheddar cheese.
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14
Cover the lasagna dish with aluminum foil and bake until the filling is bubbling, about 45 minutes.
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15
Uncover the dish and continue to bake until the cheese is browned, about 30 minutes more.
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16
Let the lasagna stand 10 minutes before serving.
