Preheat oven to 325 degrees F/160 degrees C.
In a large bowl, with a mixer on medium speed, beat the butter and sugar until smooth. Add egg yolk, liqueur, and orange peel and beat until well blended.
In another bowl, mix the flour, baking powder, and salt. Add to butter mixture; stir to mix, then beat until well blended.
Gather dough into a ball, divide it in half, and flatten each portion into a disk, then wrap each tightly in plastic wrap and freeze until firm enough to roll without sticking, about 30 minutes.
Unwrap dough. On a lightly floured surface, with a floured rolling pin, roll one disk at a time to about 1/4 inch thick. With a floured, 2-inch round cookie cutter, cut out cookies. Place about 2 inches apart on buttered 12 by 15-inch baking sheets. Gather excess dough into a ball, re-roll, and cut out remaining cookies.
In a small bowl, beat egg white with 1 teaspoon water to blend. Brush cookies with mixture and sprinkle or arrange about 1/2 teaspoon sliced almonds on each.
Bake cookies in preheated oven until lightly browned, about 15 minutes; if baking two sheets at once in one oven, switch their positions halfway through cooking. Let cookies cool on sheets for 5 minutes, then use a wide spatula to transfer to wire racks to cool completely.
Makes 3 dozen cookies.
Source: Adapted from: Sunset Magazine
Date: April 11, 2002