03Whisk eggs, cream, salt, and pepper in large bowl to blend. Add chard and cooled sausage mixture, then feta; stir to blend. Transfer mixture to prepared baking dish.
04Bake frittata until set in center, 45 to 55 minutes. Transfer baking dish to rack and cool frittata 15 to 20 minutes. Place platter atop dish with frittata. Using oven mitts, hold baking dish and platter firmly together and invert frittata onto platter; place another platter atop frittata and invert again so that frittata is right side up. Cut frittata into 20 pieces. DO AHEAD: Can be made 1 day ahead. Place frittata pieces on rimmed baking sheet. Cover and chill. Rewarm in 325°F oven until heated through, about 10 minutes.
05Transfer frittata pieces to platter. Garnish each piece with parsley; serve warm or at room temperature.