Preheat oven to 350 degrees F. Line two baking sheets with parchment paper or Silpats.
Put a 1/2 inch wide star tip in a large pastry bag and have it ready to go.
In a mixing bowl, using an electric mixer, beat the butter and sugar together until very light and fluffy. Beat in the salt, vanilla and egg yolks and mix well.
Gradually add the flour, 1/2 cup at a time, stirring until fully blended and you have a soft dough. Spoon about 1/3 to 1/2 of it into your pastry bag.
Pipe the dough into circles somewhere around 3 inches in diameter. Sprinkle generously with sparkling sugar.
Bake one sheet at a time for about 12 to 14 minutes or just until the cookies start turning golden brown around the edges. Let cool on baking sheets for 5 minutes before transferring to a wire rack.