These make for a delicious puffy coconut treat after the rehearsal dinner.
Brush a 9-by-13-inch glass baking dish with oil. Line with parchment paper, leaving a 2-inch overhang on short sides; brush with oil. Put 3/4 cup water into the bowl of an electric mixer fitted with the whisk attachment; sprinkle gelatin on top. Let stand until soft, 5 to 10 minutes.
Stir together sugar, corn syrup, salt, and 3/4 cup water in a medium saucepan over medium-high heat. Cook, stirring, until mixture reaches 238 degrees on a candy thermometer, about 10 minutes.
With mixer on medium-low speed, add syrup mixture to gelatin in a slow, steady stream. Raise speed to high; beat until mixture is cool and has tripled in volume, about 15 minutes. Beat in vanilla and coconut extracts.
Pour mixture into prepared dish; using an oiled offset spatula, spread evenly. Let stand at least 4 hours (or overnight). Lift up parchment to remove marshmallow from pan. Using an oiled knife, cut into 1-inch cubes. Coat in coconut and then in confectioners' sugar. Marshmallows can be stored in airtight containers at room temperature up to 1 week.