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1
Heat oil in a 12-to 14-inch heavy skillet over medium heat until it shimmers.
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2
Cook pancetta, onion, carrot, celery, and garlic, stirring occasionally, until vegetables are golden and softened, 12 to 15 minutes.
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3
Add beef and cook, stirring occasionally and breaking up any lumps, until meat is no longer pink, 6 to 10 minutes.
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4
Stir in wine, milk, tomato paste, thyme, 1/4 teaspoon salt, and 3/4 teaspoon pepper.
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5
Simmer, uncovered, stirring occasionally, until most of liquid has evaporated but sauce is still moist, about 1 hour.
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6
Put spinach in a kitchen towel (not terry cloth) and twist to squeeze out as much moisture as possible.
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7
Whisk together ricotta, eggs, parmesan, nutmeg, 1 1/4 teaspoons salt, and 1 teaspoon pepper.
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8
Transfer 1 1/2 cups ricotta mixture to another bowl and whisk in 1/4 cup milk; set aside.
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9
Whisk spinach into remaining filling with remaining 1/2 cup milk.
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10
Preheat oven to 375F with rack in middle.
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11
Soak noodles in a bowl of very warm water until pliable but not softened, 3 to 5 minutes.
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12
Place on a kitchen towel (it's not necessary to pat noodles dry).
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13
Spread 1 1/2 cups bolognese sauce in baking pan and sprinkle with 1 tablespoon parmesan.
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14
Cover with 3 noodles, leaving space in between.
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15
Spread half of spinach filling on top, then 1 cup bolognese sauce, and top with 1 tablespoon parmesan and 3 noodles; repeat.
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16
Top with remaining bolognese sauce, 1 tablespoon parmesan, and remaining 3 noodles.
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17
Pour reserved ricotta mixture over top and sprinkle with remaining 1/4 cup parmesan.
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18
Cover pan tightly with parchment paper and foil (or just buttered foil) and bake 50 minutes.
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19
Remove foil and bake until top is browned in spots, about 15 minutes more.
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20
Let stand 15 to 30 minutes before cutting.
