Whip butter with icing sugar, extract and salt for 3 minutes or until almost white and very creamy. Sift flour with cornstarch; gradually beat into butter mixture, one third at a time. Scrape bowl. Beat on low for 1 additional minute or until dough is well combined.
Chill dough for 20 minutes. Roll into 1-inch balls; flatten with a lightly floured fork.
Preheat oven to 325°F. Place flattened balls, 1-inch apart, on parchment paper-lined baking sheets.
Bake, in batches on bottom rack, for 12 to 14 minutes or until bottoms are golden. Cool completely on the sheet.
Garnish: Use white chocolate chips and sprinkle with crushed candy canes. For chocolate chips, melt in a heatproof bowl set over a pot of gently simmering water. Garnish as desired. Makes about 3 dozen cookies.
Store cookies, in airtight containers between layers of parchment paper, for up to 5 days. Or, freeze for up to 1 month.)