Place the cold water in a saucepan, then sprinkle the gelatin over the water and let sit for 1 minute to soften. Whisk in the coconut milk, macadamia nut milk, sweetener, vanilla bean seeds, and salt. Stir well to combine with the gelatin. Bring the mixture to a boil, then remove from the heat and let cool to room temperature.
Place a 12-cavity silicone mold on a baking sheet or other large flat surface for transporting to the fridge. Fill each mold just shy of the top with the mixture. Place in the fridge until set, about 2 hours, then transfer to the freezer for 2 hours for easy removal from the mold.
Remove the petits fours from the mold by pushing the bottom of the mold with your hands. Place on a serving platter, allow to thaw, and serve chilled, not frozen. Just before serving, drizzle with thinned, warm hot fudge sauce, if desired.
Store covered in the fridge for up to 5 days or in the freezer for up to 1 month.