Cream the butter, vanilla, salt and sugar. Next, add well-beaten eggs, then milk.
In a separate bowl, combine flour and baking powder.
Pour dry ingredients into wet ingredients and mix until incorporated.
Roll dough into ball, cover with plastic wrap, and chill for 1 hour.
Preheat oven to 325.
Roll dough to 1/8", make trefoil cutouts, sprinkle sugar crystals on top, and bake for about 12-15 minutes, or until just golden brown.