In a large mixer bowl at medium speed, beat butter and sugar. Beat in eggs and vanilla. Mix flour and baking powder and stir into butter mixture. Divide dough into thirds; shpae into balls and flatten slightly; wrap in plastic and refrigerate for 3 hours or overnight. Roll into 1/8" thickness and cut. Bake at 375 degrees for 6 minutes or almost lightly browned. Cool and decorate with Xmas Icing.