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1
Heat the oil in a large saucepan over medium heat.
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2
Add the onion, celery, carrot, red pepper, zucchini, and bacon and cook for 5 minutes, until softened.
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3
Add the beef and cook, breaking up with a spoon, about 10 minutes, until browned.
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4
Add the marinara sauce and oregano.
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5
Bring to a boil, reduce heat to low, and simmer for 5 minutes.
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6
Meanwhile, make the white sauce.
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7
Melt the butter in a saucepan over low heat, whisk in the flour, and cook for 1 minute.
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8
Whisk in the milk.
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9
Cook, whisking often, until the sauce boils.
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10
Stir in the ricotta cheese and season with salt and pepper if desired and nutmeg.
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11
Remove from heat.
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12
Preheat the oven to 375 degrees.
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13
Line a large rectangular (9 x 13 in) baking dish with heavy-duty Reynolds foil, leaving a little overhand on all four sides.
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14
Spread 1/4 cup of the white sauce on the bottom.
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15
Arrange 3 lasagna sheets in the dish and top with one third of the ragu and 1/2 cup of the white sauce.
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16
Repeat layers twice more.
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17
Top with 3 lasagna sheets, the remaining white sauce, and the Parmesan cheese.
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18
Bake for 45 minutes, until the top is golden and bubbling.
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19
Let stand 10 minutes, then serve hot.