From 'The Way Yia Yia Did It' published by St. Sophia Greek Orthodox Church in San Antonio, named after their annual 'Funstival' Cream butter with sugar in an electric mixer, adding sugar slowly. Beat 20 minutes or until the consistency of whipped cream. Add vanilla, then eggs one at a time. Beat well after each addition. Take from mixer. With a wooden spoon or rubber spatula, fold in 4 cups of flour sifted together with baking powder. Knead in remaining flour, half cup at a time, until a soft non-sticky dough is achieved. If large eggs are used, a little more flour may be needed. Pinch off dough the size of a walnut and roll pencil thin, fold in half side by side and twist. Brush with beaten egg yolk and press sesame seeds on each piece. Place on cookie sheets and bake at 180ºC or 30 minutes or until golden brown. Makes 50 to 60 cookies.