In a bowl combine the cheeses, eggs, flour, salt (unless the feta is very salty) nutmeg, and 3 tablespoons butter. Cover the bowl and chill several hours or overnight, removing from the refrigerator an hour before using. Cut the phyllo into thirds (3 x 11 inches). Pile up the phyllo, covering it with waxed paper and a damp towel. Take out one sheet at a time and keep the rest covered. Butter the phyllo, one sheet at a time, using a pastry brush and the 1 cup melted butter. Place 1 teaspoon of the filling 1 inch from the end nearest you. Fold the phyllo back over the filling so the bottom edge meets the left edge, forming a right angle. Continue folding back at right angles to make the triangular shape. Bake in a moderate oven (350 degrees) for 20 to 25 minutes or until golden and crisp, turning once. Serve hot.
Note: Tyropites may be stacked upright in cardboard boxes and frozen. When ready to bake, separate while still frozen, spread on baking sheets, and bake as directed above, allowing an additional 10 minutes baking time.
Source: The Food of Greece by Vilma Liacouras Chantiles. Avenel Books, New York. Source: Karen Mintzias - I-Cooking