Sift flour, baking powder and salt into a large bowl; set aside. Beat butter and sugar in large bowl with electric mixer on high speed until light and fluffy. Add egg, milk and sesame oil; mix well. Gradually beat in flour mixture on low speed until dough begins to pull away from sides of bowl. Stir in 1/2 cup (125 ml) of the toasted sesame seeds and black sesame seeds. Divide dough in half. Form each half into a log, about 2 inches (5 cm) in diameter. Wrap in plastic wrap. Refrigerate 2 hours.
Preheat oven to 375°F (190°C). Remove dough from refrigerator and cut into 1/4-inch (1/2- cm) thick slices. Place on parchment-lined baking sheet.
Bake 7 to 8 minutes or until edges are lightly browned. Cool on baking sheets 1 minute. Remove to wire racks; cool completely.
Dip each cookie in melted chocolate, coating about 1/3 of each cookie. Sprinkle cookies with remaining toasted sesame seeds. Let stand at room temperature on wax paper-lined tray 15 minutes or until chocolate is set.