Preheat oven to 350.
Butter 2 cookie sheets and refrigerate for 15 minutes.
Cream butter and sugar until fluffy.
Beat in egg yolks and vanilla until incorporated.
Gradually add flour and salt and mix until blended.
Transfer to a pastry bag with a star tip.
Pipe onto prepared sheet. Leave at least 1" between cookies.
Bake for 11-13 minutes or until the edges are just barely brown.
Transfer to a wire rack to cool.
In a small bowl combine chocolate chips and Crisco.
Melt by microwaving for 30 seconds and stirring, until melted and smooth.
Dip cookie half way in chocolate and set on sheet.
Sprinkle with nonpareils.