Line a 13x9" pan or large rimmed baking sheet with parchment paper, cutting from each of the four corners of the paper down to the bottom corner of the pan so that the paper lays flat. Sift 3 tablespoons or so of powdered sugar over the parchment paper.

Place 1/2 cup of the water and gelatin into the bowl of a stand mixer fitted with the whisk attachment and whisk until combined. Allow to soften 15 minutes.

In a 2 quart saucepan, place the granulated sugar, corn syrup, salt and remaining 1/2 cup water over medium low heat until the sugar has dissolved. Increase the heat to medium and bring to a boil. Cover the pot and boil for 2 minutes. Remove the lid, increase the heat to high, and boil without stirring until the mixture reaches a temperature of 240 degrees on a candy thermometer, about 10 minutes.

Turn the mixer on low, and pour the hot syrup slowly into the gelatin mixture. Gradually increase the speed to high and beat until the mixture has tripled in volume and is thick and stiff, about 10 minutes. Add the peppermint extract during the last minute of mixing time.

Scrape the mixture into the prepared pan and spread as evenly as possible. Sprinkle with 3 more tablespoons of sifted powdered sugar, and let stand uncovered for 8-12 hours.

Remove from the pan, and cut the marshmallows using a very sharp knife. Toss into sifted powdered sugar until coated, then shake off the excess. Place the marshmallows on waxed paper or parchment in a single layer.

Place the chocolate and coconut oil in a heat proof bowl and stir to combine. Microwave for 1 minute, then stir. If the chocolate hasn't completely melted, microwave for 30 seconds more and stir once again.

Drizzle the marshmallows with the chocolate and sprinkle the peppermint crunch over the top. Allow to stand at room temperature until set.

Store the marshmallows in an airtight container at room temperature for 2-3 weeks. Layer between sheets of waxed paper or parchment to prevent sticking.