Put oven rack in middle position and preheat oven to 300°F. Butter a baking sheet, then line with foil and lightly butter foil.

Stir together egg white, sugar, vanilla, almond extract, and a pinch of salt until combined, then stir in coconut. Divide coconut mixture into fourths, then drop in 4 mounds (about 2 inches apart) onto baking sheet.

Bake until tops are pale golden in spots, 15 to 20 minutes, then carefully lift foil with cookies from baking sheet and transfer to a rack to cool completely, about 15 minutes. Peel macaroons from foil.

In a double boiler, melt the chocolate and butter. Let chocolate mixture cool before dipping the tops of the macaroons.

Transfer the macaroons to a parchment-lined platter or baking sheet and place in the refrigerator for 20-30 minutes, or until the chocolate has hardened.