In a large bowl, cream together the butter and sugar.

Beat in the yolks one at a time.

Stir in the vanilla.

In separate bowl, combine flour and salt.

Mix flour mixture into the creamed mixture.

Shape dough into logs about 1 and 1/2 inches in diameter. Wrap in waxed paper or plastic wrap and refrigerate or freeze until firm.

Preheat oven to 350 degrees F (175 degrees C). Unwrap rolls. Let sit at room temperature for about 15 minutes if refrigerated, longer if frozen.

Sprinkle sparkling sugars into top of dough and gently press down. If sugars aren't sticking, allow dough to sit out a bit longer.

Cut into approximately 3/8 inch wide slices.

Place slices 2 inches apart onto parchment paper or silicone baking sheet lined cookie sheets. (Ungreased will work as well.)

Bake for 8 to 12 minutes in the preheated oven or until edges just barely start to brown. Remove to a wire rack to cool completely.

Store in air tight container.