Combine ½ cup of the water, sugar, corn syrup, and salt, in a small saucepan.
Cover the saucepan and cook over medium-high heat for 4 minutes.
While the sugar is heating up, empty the envelopes of gelatin into the bottom of your stand mixer bowl and pour in the remaining ½ cup of cold water. This step is to soften the gelatin so it reacts with the hot ingredients.
Then attach the whisk attachment to the mixer. Let this stand while you finish cooking the sugar.
Remove the lid from the sugar mixture and, using a candy thermometer, cook the mixture until it reaches 240º F, the soft ball stage. This should take about 5 to 7 minutes. Leave the sugar mixture alone, don’t stir it.
Once the liquefied sugar is up to temperature, turn the mixer to low speed and slowly pour the sugar mixture down the side of the bowl into the gelatin. Be careful not to pour this over the whisk while it is running or you may get splattered with hot sugar!
When all the sugar is combined with the gelatin, turn the mixer to high speed and whip for 13 to 15 minutes. The bottom of the bowl will go from hot to lukewarm and the mixture will be very thick.
During the last minute of whipping, add the vanilla.