12 ounces Swiss chard
1 tablespoon olive oil
1 sweet onion, peeled and cut into thin wedges
1/8 teaspoon ground nutmeg
Salt and pepper
1 pound purchased or home-made pizza dough, at room temperature
1 cup ricotta cheese
2/3 cup grated parmesan cheese
1/3 cup drained chopped oil-packed dried tomatoes
1/4 cup toasted pine nuts (see "Toasting Nuts," below)
1/4 teaspoon red chile flakes (optional)
Preheat oven to 450°. Trim and discard chard stems; roughly chop leaves. Pour olive oil into a 10- to 12-inch frying pan over medium-high heat. When hot, add onion and stir often until softened, about 4 minutes. Add chard, sprinkle with nutmeg, and season to taste with salt and pepper. Stir until wilted, 3 to 5 minutes; set aside.
On a lightly floured surface, divide dough into four equal pieces. Using a lightly floured rolling pin or your hands, roll or stretch each piece into a 6-inch round. If dough shrinks, let it rest about 5 minutes, then roll again. In a small bowl, mix ricotta, parmesan, dried tomatoes, pine nuts, and chile flakes (if using). Season with salt and pepper to taste. Mound equal portions of ricotta mixture in center of dough rounds. Top with chard mixture.
Gently pull half of dough over filling to make a half-moon shape. Fold bottom edge of dough over top edge and pinch firmly to seal. Brush tops of calzones lightly with olive oil. Transfer to a large baking sheet.
Bake calzones on middle rack until golden brown, 20 to 25 minutes (15 to 20 minutes in a convection oven). Let cool about 5 minutes, then transfer to plates.