Grandma's Butter Cookies

1 cup butter
1 ½ cup sugar
2 egg yolks
1 tsp. Soda (dissolved in 1 tbsp hot water)
2 cup flour
1 tsp cream of tartar
1 tsp vanilla

Mix all together adding vanilla last. Shape into small balls and place 2 inches apart on cookie sheet. Bake at 375 degrees for 15 minutes.