01 - Lightly grease a 9x9-inch baking pan. Line it with parchment paper and dust evenly with a mixture of powdered sugar and cornstarch.
02 - In a stand mixer bowl, combine gelatin with 1/2 cup cold water. Allow to soften while preparing the sugar syrup.
03 - In a medium saucepan, combine remaining 1/2 cup cold water, granulated sugar, corn syrup, and salt. Heat over medium, stirring until sugar dissolves. Increase heat and boil without stirring until mixture reaches 240°F (115°C) on a candy thermometer.
04 - With the mixer on low speed using the whisk attachment, slowly pour the hot syrup into the gelatin mixture.
05 - Increase mixer speed to high and beat for 10 to 12 minutes until the mixture is thick, glossy, and has tripled in volume. Add vanilla extract and mix briefly to incorporate.
06 - Quickly fold in 1/2 cup mini chocolate chips by hand, ensuring even distribution without deflating the mixture.
07 - Pour the marshmallow mixture into the prepared pan, spreading the surface smoothly. Sprinkle additional mini chocolate chips on top and gently press them in.
08 - Dust the surface with the powdered sugar-cornstarch mixture. Allow to set uncovered at room temperature for at least 90 minutes until firm.
09 - Invert onto a cutting board. Dust a sharp knife with the powdered sugar-cornstarch blend and cut into 16 equal squares.
10 - Toss the squares in remaining powdered sugar-cornstarch mixture to prevent sticking.