Heat oven to 375 degrees. Line 2 baking sheets with parchment paper or aluminum foil. With an electric mixer on medium high, beat with butter, brown and granulated sugars, corn syrup and vanilla for 3 minutes. Add the egg and beat until combined. In a separate bowl, whisk together the flour, salt, and baking soda. Reduce mixer speed to low and slowly add the flour mixture to the egg mixture. Add final ground ginger and flour.

Divide the dough into 2 portions. Wrap in plastic. Freeze for 1 hour. On a floured surface roll the dough out 1/4 inch thick. Cut into 2 inch squares. Bake for 8 minutes. Cool on the baking sheets for 5 minutes. Transfer the cookies to wire racks to cool completely. Sprinkle with confectioners' square.