In a medium bowl whisk together cornstarch and confectioners' sugar. Pour into sieve and set aside.
Prepare a 13x9x2 inch baking pan by spraying with cooking spray and adding 1/4 cup of cornstarch/sugar mixture over top and ensuring even coverage of pan. (similar to preparing a cake pan)
Attach whisk to Breville Baker Chef
Pour 3 pouches of gelatine into bottom of mixing bowl and pour 1/2 cup ice cold water over it.
In a medium saucepan add 1/2 cup water, granulated sugar, corn syrup and salt. Cover and cook over medium high heat for 4 minutes. Uncover and clip a candy thermometer on the pan and cook until temperature reaches 240F. Watch closely to prevent boiling over. Immediately remove from heat once it reaches temperature.
Attach splash cover to mixing bowl and turn Bakery Chef to low. Slowly pour hot syrup through splash cover spout. Once all syrup has been added, turn mixer to high and whip until lukewarm and thick, approximately 7 to 8 minutes. Add vanilla at very end.
Using spatula light sprayed with cooking spray, spread marshmallow mixture into prepared pan. Dust with another 1/4 cup of cornstarch/confectioners' sugar and set aside for 24 hours.
When ready to cut, prepare a cutting board by spreading cornstarch/confectioners' sugar mixture on board. Run a warm knife around edges of pan and invert onto cutting board. Tap bottom (be patient, it will fall out).
Mark one inch increments along sides and using either a chef's knife or pizza cutter lightly dusted with cornstarch/confectioners' sugar mixture cut into one inch squares.
Lightly dust all sides of each marshmallow with cornstarch/confectioners' sugar.
Store between pieces of wax paper dusted with more cornstarch/confectioner's sugar in an airtight container. Serve with hot cocoa, use for smores, or add to cello bag tied with a ribbon and gift a few.