Sift the flour and salt into a large bowl and make a well in the middle. Pour in the egg, oil, and club soda and stir into the flour, adding more club soda if necessary, ot make a rather soft dough. Transfer the dough to a floured board and knead until smooth and elastic, about 10 minutes. Shape the dough into a ball, cover with a linen or cotton (not terry cloth) kitchen towel and let stand for 1 hour. Divide the dough into four parts and shape each one into a ball. Let stand, covered, for 15 minutes. Preheat the oven to 180ºC . and butter two large baking sheets. On a floured surface, roll out one of the balls into an 0 cm thick square. Brush the dough with some of the melted butter Dip your fingers into the melted butter and pull the edges of the dough in different directions, stretching it evenly until it is almost transparently thin. Don't worry if the dough tears, as you will be folding it up. With a sharp knife, trim the edges of the dough to from an even square. Fold the square in half, brush the surface generously with the melted d fold in half again crosswise to from a smaller square. It should be approximately 6 to 18 cm. It is isn't, pull it out slightly to fit the dimensions. Brush the square with butter. Shape one-fourth of the filling into a ball and place in the center of the square. Fold in the corners of the square like an envelope. With the palm of your hand, flatten the pie so it is about 3 cm thick. Brush the top with melted butter and carefully transfer to a prepared baking sheet. Repeat the procedure with the rest of the dough and filling. Bake the pies in the middle of the oven, until golden brown, about 35 minutes. Serve warm. Makes 4 Pies for 8 Servings RED BEAN FILLING: Drain the beans and place them in a saucepan along with enough fresh water to cover by at least 5 cm. Bring to a boil and add salt, then reduce the heat to medium-low. Cook the beans, partially covered, until almost mushy, about 1.5 hours. While the beans are cooking, heat the oil in a medium size skillet, over medium heat, and add the onion to saute it. Stir occasionally, until dark brown, about 15 to 20 minutes. When the beans are done, drain well and mash. Add the sauteed onions and their cooking fat and the cilantro. Season generously with salt and freshly ground black pepper. Cool to room temperature. Makes enough filling for 4 pies.