Preheat oven to 350F. In a large bowl, beat the butter until it is smooth. Add the confectioners sugar and beat again until fully combined and smooth again. Add the salt, yolks and vanilla. Mix well. Add the flour and mix just until combined.

Turn the dough out on the counter and divide into four even pieces, and place each quarter in a small bowl. Add mix-ins as desired to each quarter.

Turn one quarter out onto the counter that has been lightly dusted with confectioners sugar. Roll the dough into a sausage about 2 inches in diameter. For bakery style sizes, roll into a fatter log. Do the same with the remaining dough.

Wrap each log in plastic wrap and refrigerate for at least 2 hours or overnight. Once chilled, unwrap a log, roll it in any nuts or coatings, and slice it into rounds approx. 1/2 inch thick. Place cookies about 1 inch apart, on a sheet lined with parchment, and bake for 12-14 minutes. Allow cookies to rest for 2 minutes before moving to a cooling rack.

Melt the chocolate chips and shortening in a microwave safe dish. Stir until smooth. Garnish cookies with melted chocolate and chopped nuts, chopped chocolate bars, or coconut if desired.