6 ounces bittersweet or semisweet chocolate, melted and cooled to room temperature
Heat oven to 325° F.
In a medium bowl, combine the coconut, egg whites, sugar, flour, salt, and vanilla.
Drop packed tablespoonfuls of the mixture onto parchment-lined baking sheets, spacing them 1 inch apart. Using slightly wet fingertips, gently form each cookie into a smooth dome shape.
Bake, rotating the baking sheets halfway through, until lightly golden, 25 to 30 minutes. Cool slightly on the baking sheets, then transfer to wire racks to cool completely.
When cool, dip the bottom of each macaroon in the chocolate and place on a parchment-lined baking sheet. Refrigerate until firm, 20 to 30 minutes. Store the macaroons in an airtight container at room temperature for up to 7 days.