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1
Preheat oven to 400F.
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2
Whisk together ricotta, eggs, 1/2 teaspoon salt, and 1/4 teaspoon pepper.
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3
Squeeze spinach to remove as much liquid as possible, and add to ricotta mixture; stir well to combine.
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4
Spread a thin layer of tomato sauce in the bottom of a 9-by-13-inch glass baking dish.
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5
Arrange 4 noodles on top.
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6
Spread one-third of the ricotta mixture over noodles, followed by one-third of the remaining tomato sauce; sprinkle with one-third of the fontina cheese.
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7
Repeat to make two more layers, ending with fontina.
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8
(At this point, the lasagna can be tightly wrapped in plastic and frozen up to 2 months.
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9
Thaw overnight in the refrigerator before proceeding.)
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10
Cover with aluminum foil; bake 30 minutes (40 minutes if previously frozen).
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11
Remove foil; continue baking until golden brown on top and sauce is bubbling, about 15 minutes more.
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12
Let cool slightly before cutting into squares and serving.
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13
Remove casings from hot or sweet Italian sausage (you will need about 1 pound for a large lasagna and 8 ounces for a small one).
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14
Cook in a medium skillet over medium heat, breaking up meat with a spoon, until no longer pink, about 10 minutes.
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15
Let cool.
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16
Follow recipe above, layering sausage in thirds after the tomato sauce.
