1Line 2 cookie sheets with cooking parchment paper. In large bowl, beat butter with electric mixer on medium speed until creamy. Gradually add granulated sugar, beating until blended. Beat in egg and vanilla. On low speed, beat in flour, baking powder and salt. Divide dough in half; shape each half into a ball and flatten slightly. Wrap in plastic wrap; refrigerate until firm, about 2 hours.
2Heat oven to 375°F. Unwrap 1 portion of dough; keep remaining dough in refrigerator. Shape dough into 1 1/2-inch balls; heavily roll in sanding sugars. On cookie sheets, place balls 2 inches apart. Barely flatten cookies to about 1-inch thickness using palms. Repeat with remaining dough.
3Bake 13 to 15 minutes or until edges are golden brown. Cool 5 minutes; remove from cookie sheets to cooling racks.