1. In a large bowl, whisk together flour, sugar, baking powder and salt. In a second large bowl, beat butter and sugar until smooth, about 2 minutes. Beat in egg and coconut and vanilla extracts. On low speed, beat in flour mixture until just combined.
2. Gather dough; divide in half. Form each half into a disk. Wrap tightly in plastic wrap. Refrigerate 4 hours or as long as overnight.
3. Heat oven to 350 degrees F. Roll 1 heaping teaspoon dough into a ball. On a well-floured work surface, flatten with a cup. Transfer to an ungreased baking sheet. Repeat with remaining dough.
4. Bake at 350 degrees F for 10 to 12 minutes. Cool on wire rack. Melt bittersweet chocolate. Dip an edge of one cookie in chocolate; rotate cookie slightly and dip again. Repeat with all cookies and place on waxed-paper-lined baking sheets. Sprinkle with toasted coconut; let chocolate set at least 15 minutes.