Allow butter and egg yolk to stand at room temperature for 30 minutes.
In a large mixing bowl, beat the softened butter with an electric mixer on medium to high speed for 30 seconds. Add 2/3 cup sugar; beat about 5 minutes or until well-combined and very fluffy, scraping sides of bowl occasionally. Add egg yolk, cardamom, baking soda and salt. Beat until combined. Beat in as much of the flour as you can; stir in any remaining flour with a wooden spoon. Cover and chill dough about 1 hour or until easy to handle.
Shape dough into 1-inch balls. Place 2 inches apart on ungreased cookie sheets. Bake in a 350 degrees F oven about 10 minutes or until edges are just set and bottoms are very lightly browned. Let cookies cool on sheets for 1 minute. Transfer to wire racks; cool completely. Gently dip cookies in 1/2 cup extra-fine sugar, turning to coat all sides.