1) Lightly grease two baking sheets, or line them with parchment.
2) In a large bowl, beat together the eggs, salt, confectioners' sugar and flavor for 5 to 6 minutes, until the mixture is very light and falls in thick ribbons from the beater.
3) Gradually beat in the flour to form a stiff dough.
4) Transfer the dough to a well-floured work surface and knead with your hands for several minutes — it will seem dry at first, but will become smooth as you work with it. Wrap the dough in plastic wrap and let it rest at room temperature for 30 minutes or so.
5) To shape cookies using a springerle pin: Dust your work surface lightly with flour. Divide the dough in half and work with one piece at a time, leaving the other piece covered. Use a regular rolling pin to roll the dough into a 1/4"-thick rectangle, roughly the same size as your springerle pin.
6) Use a pastry brush to brush a very light coating of flour onto the dough. Flour your springerle pin, then give it a couple of sharp raps to knock off excess. Slowly roll the springerle pin over the dough, pressing down hard enough to leave a good impression. Cut the cookies apart on the lines, with a pizza wheel or sharp knife.
7) To shape cookies using a springerle mold: Lightly dust your work surface. Dust the mold with flour, then tap it firmly to remove excess. Divide the dough in half and work with one piece of dough at a time, leaving the other covered. Roll the dough into a 1/4"-thick square or rectangle
8) Press the lightly floured mold firmly into the dough. Remove the mold and cut around the design with a knife. Repeat until all the dough is cut.
9) Transfer the cookies to the prepared baking sheets. If you're using anise seed, sprinkle it on the cookie sheet or the parchment before laying down the cookies, giving them extra flavor. They'll also raise the cookies just a bit, allowing air to circulate around the bottom, drying them thoroughly.
10) Set the unbaked cookies aside to dry at room temperature, uncovered, for 24 hours. Turn them over once during the drying time to allow the bottoms to dry.
11) Preheat the oven to 275°F.
12) Bake the cookies for 25 to 30 minutes, until they're firm but not brown. (If the cookies are a bit puffy, and the design isn't as sharp as you'd like, bake the next batch at 250 degrees for 35 to 40 minutes.) Remove them from the oven and transfer to a rack to cool completely.
13) Store the cookies in an airtight container. To keep them from becoming rock hard, we suggest placing a piece of soft bread, a slice of apple, or a cookie softener in the container with them.
Yield: 2 1/2 to 3 dozen cookies.