In a large bowl combine the butter and sugar and beat with a wooden spoon (or alternately, cream the butter and sugar in an electric mixer that is fitted with a paddle attachment). Add the egg yolks and vanilla extract, mix until combined. In a separate bowl, mix together the salt, baking soda, and flour, mix well then add this mixture to the first bowl. Mix the dough until it forms dough, then knead together just until it forms a smooth ball. Wrap the dough in cellophane and refrigerate it for at least 1 hour.
Preheat an oven to 350 degrees Fahrenheit. Roll the dough out to approximately 1/4 inch thick and cut into desired shapes. Bake the cookies on a lightly oiled cookie sheet in the preheated oven for approximately 10 minutes, or until light golden-brown. Cool on a wire rack and, if desired, ice the cookies with a simple sugar icing or drizzle with melted chocolate.