Grease and flour a baking sheet pan or stone. Cream butter, sugar, egg yolks, and vanilla, beat until smooth. Add Flour, mix well. Mix in beaten egg white and baking powder. Pour batter onto greased and floured pan, spread to even out and get into the corners of the pan. Level as best you can. Sprinkle with a bit of granulated sugar on top, before baking.
2) Bake at 325 º to 335 º for 20 minutes. They are done when a toothpick is inserted in and comes out dry. Let cool and sprinkle with 10X sugar. Cut into crescent moons using a glass. Using the glass opening cut a full circle in one of the corners of the pan, that first cookie is yours to eat. Then begin moving the glass in a straight row, a little at a time, shaping the cookies into crescent moons. These cookies make a beautiful presentation for company, and freeze well.