Combine the powdered sugar and corn starch and dust about half the mixture over the surface of the parchment lined pan.
Combine the gelatin and ½ cup water in the mixing bowl of a stand mixer and set aside.
Combine the sugar, corn syrup, and remaining 1 cup of water in a saucepan and heat over med-high heat until the mixture reaches 240℉ on a candy thermometer.
Start the mixer on low speed using the whisk attachment and slowly stream the hot sugar mixture into the gelatin.
Once the sugar mixture has been fully streamed in, slowly increase the mixer speed until it reaches full speed.
Once at full speed, beat the mixture for 8 minutes.
With the mixer still running, add in the caramel and continue beating for another minute.
Pour the marshmallow mixture into the prepared pan, and top with the remaining cornstarch mixture.
Let set for 4 hours, then cut into cubes and enjoy!
Notes
Increasing the mixer speed slowly will help avoid splatter. The mixer may need to run for a minute or two at some interim speeds before increasing to the next speed. Remember to use caution as the mixture will be hot!The caramel sauce should not fully combine into the marshmallow mixture, it should jut swirl throughout the marshmallow mixture. If the caramel sauce does fully mix in, the marshmallows will still come out great, the caramel flavor will just be more subtle. If the caramel is not swirled in enough the marshmallows will likely be wet and may not keep.