Prepare pan and gelatin: Line an 8×8-inch pan with parchment paper and lightly dust with powdered sugar or cornstarch. In a small bowl, sprinkle gelatin over 1/2 cup cold water and let it bloom for 5–10 minutes.
Make honey syrup: In a saucepan, combine honey, 1/2 cup water, and salt. Heat over medium heat until it reaches 240°F (soft-ball stage) on a candy thermometer. Remove from heat.
Combine and whip: Pour the hot honey syrup slowly into the bloomed gelatin while mixing on low speed. Once combined, increase mixer speed to high and whip for 10–15 minutes until the mixture is thick, glossy, and tripled in volume. Add vanilla extract in the last minute of whipping.
Set the marshmallows: Pour the marshmallow mixture into the prepared pan, smooth the top, and let it set at room temperature for at least 4 hours or overnight.
Cut and dust: Remove marshmallow slab from the pan, peel off parchment, and cut into squares. Dust each piece with powdered sugar or cornstarch to prevent sticking.
