These are very distinctive, delicious mini marshmallows that will be wonderful on the Viennese coffee float served at your wedding reception.
Brush a 13-by-9-inch rimmed baking sheet with oil. Sift cocoa powder over sheet to cover completely. Set aside.
Put 3/4 cup cold water into a small heatproof bowl, and sprinkle with gelatin; let stand until gelatin has softened, about 5 minutes. Set over a pan of simmering water; whisk until gelatin has dissolved. Whisk in coffee extract and orange-flower water. Cover, and remove from heat.
Put sugar, corn syrup, and 3/4 cup water into a medium saucepan. Cook over medium heat, whisking occasionally, until sugar has dissolved. Continue to cook, without stirring, until syrup comes to a boil, washing down sides of pan with a wet pastry brush to prevent crystals from forming. Let boil, gently swirling pan occasionally, until mixture registers 260 degrees. On a candy thermometer (hard-ball stage), 7 to 10 minutes. Remove from heat; whisk in gelatin mixture.
Meanwhile, put egg whites into the bowl of an electric mixer fitted with the whisk attachment; beat on medium speed until foamy. Reduce speed to medium-low. Carefully add hot syrup, pouring it down side of bowl to prevent spattering. Gradually raise speed to high; beat until mixture is cool and stiff peaks form, about 20 minutes.
Pour into prepared baking sheet; immediately smooth top with an offset spatula. Sift cocoa powder over top. Let stand, uncovered, at room temperature until firm, about 3 hours.
To unmold, run a knife around edges; invert onto a piece of parchment. Lightly brush a sharp knife with oil; trim edges, and cut into 1/2-inch cubes. Sift cocoa powder into a small bowl; roll each cube in cocoa powder to coat.