2 pounds (906g) high-quality milk chocolate, finely chopped
1½ tablespoons (21g) coconut oil
2½ teaspoons (7g) powdered gelatin
1 cup (198g) granulated sugar
Pinch of fine sea salt
1 tablespoon pure vanilla extract
1. Place 20 paper or silicone muffin liners on a baking sheet.
2. Place the chocolate and coconut oil in a medium heat-safe bowl. Place the bowl over a medium pot of simmering water, and heat until smooth and fully melted. Remove the bowl from the pot.
3. Spoon 2 tablespoons of the melted chocolate into each muffin liner. Use a small spatula or the back of a small spoon to draw the chocolate up the sides of the liners to evenly coat them. Let set for 30 minutes until firm. Reserve the remaining chocolate mixture.
4. Place ⅓ cup cool water in the bowl of an electric mixer fitted with the whisk attachment and sprinkle the gelatin over the water to bloom it.
5. Meanwhile, in a small pot, stir together the sugar, salt and 3 tablespoons water over medium heat. Continue stirring; once the sugar begins to melt and the mixture simmers, stop stirring and let it boil until a candy thermometer reads 235°F. Pour the syrup over the bloomed gelatin in the bowl of the stand mixer.
6. Whip the mixture on medium speed until thick and white, 5 to 6 minutes. Add the vanilla extract and whip for 1 minute more. Transfer the marshmallow filling to a piping bag or disposable zip-top bag. (It can be helpful to grease your spatula with nonstick spray before using it to transfer the filling.)
7. Cut a ½-inch opening from the tip of the bag. Pipe the marshmallow into the prepared cups, filling to about ¼ inch under the edge of the top rim. Let set for 15 minutes.
8. Warm the remaining chocolate mixture over the pot of simmering water until melted and smooth, if necessary. Spoon about 1 tablespoon of the melted chocolate on top of the marshmallow in each cup. Let set for 30 minutes until firm before serving.