The shells hold and reheat well, which makes them great for entertaining.
Drain and rinse under cold water.
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.
If using thawed frozen, add it to the onions and toss to mix well.
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.
- Daily Values (DVs) are the recommended amounts of nutrients to consume each day.
(-) Information is not currently available for this nutrient.
