Makes 2 dozen 1½" marshmallows
- 4½ tsp. unflavored powdered gelatin (2 to 3 packets)
- ½ cup confectioners' sugar
- ¼ cup cornstarch or potato starch
- ¾ cup sugar
- ½ cup light corn syrup
- ⅛ tsp. kosher salt
- 2 tsp. pure vanilla extract
- 10 ounces bittersweet chocolate chips
Active time: 45 minutes
Total time: 7 hours
Lightly coat an 8" x 8" baking pan with cooking spray. Whisk together gelatin and ½ cup cold water in a small bowl and set aside 5 minutes. Meanwhile, make coating: Sift together confectioners' sugar and cornstarch or potato starch in a bowl and stir to combine. Set aside.
In a medium saucepan, stir together sugar, corn syrup, ¼ cup water, and salt. Bring sugar mixture to a boil over medium-high heat. As it's coming to a boil, dip a pastry brush in water and brush down sides of pot to remove any sugar residue. Cook until temperature reaches 240° (check with a candy or meat thermometer). Meanwhile, microwave gelatin on high until melted, 20 to 30 seconds. Pour into bowl of a stand mixer fitted with whisk attachment, set mixer speed to low, and keep it running.
Slowly pour sugar syrup into mixer bowl. Increase speed to medium and beat 5 minutes. Increase to medium-high and beat 5 more minutes. Beat on the highest setting 1 to 2 minutes more, then beat in vanilla. The finished marshmallow should now be opaque white, fluffy, and tripled in volume. Pour into prepared pan, using a rubber spatula to smooth into the corners. Sift ¼ cup coating evenly and generously over top. Let set, uncovered, at least 6 hours or overnight in a cool, dry place.
Use a knife to loosen marshmallow from edges of pan. Invert slab onto a coating-dusted work surface and dust it with more coating. Cut into whatever size pieces you wish (a pizza cutter works well). Dip sticky edges of marshmallows in more coating, patting off excess.
Melt chocolate and let cool slightly. Dip bottom half of each marshmallow in melted chocolate and place chocolate side up on a baking sheet. Refrigerate until chocolate is firm, about 10 minutes.