PLACE flour and salt in a medium-size bowl. Place coffee granules in a small plastic bag. Using a rolling pin, crush coffee granules until finely ground. Measure out 1 tsp (5 mL) and stir into flour. In a large bowl, using a wooden spoon, beat butter with sugar until evenly mixed. Gradually stir in flour mixture just until mixed. Divide dough into 2 portions, then form into small logs. Dough will be too soft to roll out. To firm up, cover and refrigerate up to 30 minutes before rolling.
WHEN ready to bake, preheat oven to 275F (140C). Line a baking sheet with parchment paper or spray with oil. For easy rolling, place a log between 2 sheets of waxed paper. Roll into a 9×6-inch (23×15-cm) rectangle. Trim edges to make them straight. With longer edge facing you, cut in half horizontally, then cut each half into thick strips about 1 1/2 inches (3.5 cm) wide.
PLACE strips on baking sheet. Bake in centre of preheated oven until cookies are firm to the touch, 25 to 30 minutes. Cool on a rack. Store in an airtight container in a cool place or refrigerate up to 1 week or freeze up to 1 month. Sprinkle with icing sugar just before serving.
Decorating tip: To create an icing-sugar star pattern, place a few tiny star-shaped confetti on one cookie. Sift icing sugar overtop, then carefully remove confetti. Repeat with remaining cookies.