1. Prepare Your Pan: Lightly spray a 9" x 11" rectangular baking dish and line it with parchment paper, leaving extra length on the sides for easy lifting later.
2. Bloom the Gelatin: In the bowl of a stand mixer (fitted with the whisk attachment), combine the gelatin and the cold ⅔ cup of water. Let this mixture sit undisturbed for about 5-10 minutes to allow the gelatin to "bloom."
3. Craft the Sweet Syrup: In a medium saucepan, bring the remaining ⅔ cup of water to a boil. Remove it from the heat, then stir in the honey, vanilla extract, and sea salt. Let it boil gently for just 1 minute.
4. Whip to Perfection: Carefully pour the hot honey mixture into the stand mixer bowl with the bloomed gelatin. Begin mixing on low speed for about a minute to combine. Then, increase the mixer speed to high and beat continuously for 8-10 minutes. The mixture should become very thick, voluminous, and shiny, resembling soft peaks of whipped egg whites.
5. Set and Chill (Naturally): Quickly transfer the fluffy marshmallow mixture into your prepared pan, using a rubber spatula to spread it evenly. Let it set at room temperature for a minimum of 2 hours, or ideally 4-5 hours, or even overnight. Avoid refrigerating.
6. Cut and Enjoy: Once the marshmallow slab is firm, generously dust your countertop or a large cutting board with arrowroot starch or powdered sugar. Invert the marshmallow slab onto the dusted surface. Use a sharp, lightly greased knife to cut it into approximately 30 pieces. For an extra touch of sweetness, dust the cut marshmallows with more arrowroot starch or powdered sugar.