Line 9 x 9-inch or 8 x 8-inch pan with plastic wrap and lightly oil it using your fingers or non-stick cooking spray. Set aside.
In the bowl of an electric mixer, sprinkle gelatin over 1/2 cup cold water. Soak for about 10 minutes.
Meanwhile, combine sugar, corn syrup and 1/4 cup water in a small saucepan, whisking only until the sugar is dissolved. Bring the mixture to a rapid boil. As soon as it is boiling, set the timer and allow to boil hard for 1 minute without stirring.
Carefully pour the boiling syrup into soaked gelatin and turn on the mixer, using the whisk attachment, starting on low and moving up to high speed. Add the salt and beat for between 10 and 12 minutes, or until fluffy and mostly cooled to almost room temperature. After it reaches that stage, add in the extract and beat to incorporate.
Grease your hands and a rubber or silicone scraper with neutral oil and transfer marshmallow into the prepared pan. Use your greased hands to press the marshmallow into the pan evenly. Take another piece of lightly oiled plastic wrap and press lightly on top of the marshmallow, creating a seal. Let mixture sit for a few hours, or overnight, until cooled and firmly set.
Sprinkle a cutting surface very generously with confectioner's sugar. Remove marshmallow from pan and lay on top of the sugar. Dust the top generously with sugar as well. Use a large, sharp knife to cut into squares. Separate pieces and toss to coat all surfaces with the sugar.
Store in an airtight container.