Put your butter and your sugar in a mixing bowl. Cream until fluffy. Add your egg yolks and mix in. Add vanilla and mix.
In a seperate bowl, mix your flour and salt. Add your dry ingredients to your wet ingredients and mix together.
Once your mix is together, start making small 1″-1 1/2″ balls of dough. Place the dough balls on your cookie sheet. Bake for 10-12 minutes. The bottoms will be golden brown. The tops are a little tougher to see, but they will be done if the bottoms are. Immediately after pulling the cookies out of the oven, use the back of a measuring spoon to make a round indention in each cookie.
For the icing, mix together your confectioners sugar and 1 tablespoon water. If you need more water, add some, but don’t make the icing too runny. Divide the icing into two bowls and add color until you get the color you are looking for. Use a spoon to fill your cookies with icing.