Spray a half sheet pan liberally with pan spray. Evenly sift on a thick layer of cornstarch across the bottom and the sides of the pan. Set aside.
In the bowl of your stand mixer fitted with the whisk attachment, place ½ cup of the cold water and the granulated gelatin.
Stir to combine and set aside.
In a 3 quart saucepan, combine the rest of the cold water, the sugar, salt, honey and corn syrup.
Bring to a boil, put the lid on the pan, and allow to boil for a minute. Note: Because of the impurities in the honey, the syrup will expand quite a bit more than you think it will, so use a pan that seems much larger than you think necessary.
Remove the lid and cook the syrup to 240F. Check the temperature by using a clip-on candy thermometer or testing frequently with an instant read thermometer.
Once the syrup reaches 240F, immediately turn the mixer on low speed and pour all the syrup into the bowl, letting it run down the inside of the bowl rather than pouring it onto the whisk.
Slowly turn up the speed to medium and then high speed and whip until the marshmallow has tripled in volume and is very thick and shiny, about 10 minutes. Add the vanilla and continue to whip for a minute to incorporate.
Spray a silicone spatula with pan spray and scrape the marshmallow onto the prepared sheet pan. Spray the back of an offset spatula with pan spray and use that to spread the marshmallow evenly in the pan.
Sift a liberal amount of confectioners’ sugar evenly over the marshmallow (enough so you cannot see any shiny marshmallow under the thick coating of sugar.
Let the marshmallow sit out at room temperature, uncovered, for 12 hours.
Cut around the edges of the marshmallow and turn it out onto a clean work surface. Brush off the excess sugar and cornstarch, and put it in a large self-sealing bag.
Use a pizza cutter to slice the finished marshmallow into 1 ½” squares.
Place a few cut marshmallows at a time into the bag and shake to coat the cut sides with the cornstarch/confectioners’ sugar mixture. Store in the bag at room temperature for up to a week.