For the Dough:.
In a bowl, combine the flour, lard, butter and salt. Mix lightly with your fingers until the mixture forms pea-sized pieces. Using a fork, stir in the ice water, a little at a time, until a dough forms, and then knead lightly until it comes together in a ball. Wrap in plastic wrap and refrigerate for at least 1 hour or as long as overnight.
For the Filling:.
In a large frying pan over medium heat, warm the olive oil. Add the onion, salt and pepper and sauté until the onion is soft and begins to turn lightly golden, 7 to 10 minutes. Add the chard stems and cook for 1 to 2 minutes. Then add the chard leaves and cook, stirring, until tender, 3 to 4 minutes. Transfer to a bowl and let cool. Add the cheeses and lime juice and mix well. Taste and adjust the seasonings.
On a lightly floured board, roll out the dough about 1/8 inch thick. Using a 3 inch round cookie cutter, cut out 12 rounds. Place about 2 teaspoons of the filling on ½ of each round, leaving a ½ inch border. Dampen the edges of the dough with a little of the egg glaze, then fold the dough over to enclose the filling. Seal the edges by pressing firmly with the tines of a fork. Arrange the empanadas on a tray, cover with plastic wrap and chill for at least 30 minutes or up to 3 days before baking.
Preheat an oven to 350 degrees F. Place the empanadas on a baking shee. Brush the tops with the egg glaze and sprinkle with cracked pepper. Using a sharp knife, cut 2 or 3 small slits in the top of each empanada to allow steam to escape.
Bake until golden, about 30 minutes. Transfer to a rack to cool. Serve warm or at room temperature.