CHEESE AND SPINACH STUFFED SHELLS

CHEESE AND SPINACH STUFFED SHELLS
24 (8 ounces) jumbo pasta shells
1 1/2 teaspoons extra-virgin olive oil
2 onions, finely chopped
2 pounds fresh spinach, trimmed and washed, or two 10-ounce packages
frozen chopped spinach, thawed and squeezed dry
2 cups part-skim ricotta cheese
2/3 cups plain dry breadcrumbs
1/2 cups freshly grated Parmesan cheese, divided
1/4 teaspoon ground nutmeg
1/8 teaspoon salt
Freshly ground pepper to taste
1 large egg white, lightly beaten
3 cups prepared marinara sauce, preferably low-sodium

Preheat oven to 375°F. Cook shells in a large pot of boiling water, stirring often, until just tender, about 15 minutes or according to package directions. Drain and rinse under cold water. Set aside.

Heat oil in a large nonstick skillet over medium-high heat. Add onions and cook, stirring occasionally, until softened, about 3 minutes. If using fresh spinach, add it in batches and toss with tongs until wilted. Drain in a colander, pressing out excess moisture with the back of a spoon. Let cool. If using thawed frozen, add it to the onions and toss to mix well. Set aside.

Combine ricotta, breadcrumbs, 1/4 cup Parmesan, and nutmeg in a bowl; mix well. Add the reserved spinach and season with salt and pepper. Stir in egg white.

Stuff each of the reserved shells with a generous 2 tablespoons of the ricotta mixture. Spread 1 cup marinara sauce in the bottom of a 9-by-13-inch baking dish. Arrange the stuffed shells in a single layer. Top with the remaining 2 cups of the sauce and sprinkle with the remaining 1/4 cup Parmesan cheese. Bake until the top is golden and the shells are heated through, about 30 minutes. (If the top browns too quickly, tent loosely with foil.) Let cool for 10 minutes before serving.