"The comforting, crowd-pleasing casserole is filled with tender pasta, melted cheese, marinara sauce, and sweet Italian sausage...."
INGREDIENTS
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1 medium yellow onion
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3 cloves garlic
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2 ounces Parmesan cheese, finely grated (about 1/2 cup)
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8 ounces full-fat, low-moisture mozzarella cheese, shredded (about 2 cups), divided
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2 tablespoons olive oil
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1 pound uncooked sweet Italian sausage, preferably bulk
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1/4 teaspoon red pepper flakes
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1 (about 24-ounce) jar marinara sauce
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1/2 teaspoon kosher salt, plus more for the pasta
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1/2 teaspoon freshly ground black pepper
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1 pound dried mostaccioli or penne pasta
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1 large egg
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1 1/2 cups whole-milk ricotta cheese
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12 large fresh basil leaves