Coat the inside of your desired mold with the chocolate. Place the mold in the fridge (or at room temperature, if using candy melts) for the chocolate to set, about 20 minutes.

Make the marshmallows: Pour 1/3 cup of cold water into the bowl of an electric mixer and sprinkle the powdered gelatin on top. Let sit for 5 minutes.

Place the sugar and ¼ cup cold water in a small pot and set to medium-high heat. Stir until the sugar has melted. Attach a candy thermometer to the pot and boil the sugar until it reaches 238F. Brush the sides of the pot with a wet pastry brush if sugar crystals stick to the sides.

Add the hot sugar to the gelatin and stir the mixture by hand, whisking for a few minutes to slightly cool. Beat with an electric mixer on medium-high speed for 8-10 minutes, until soft peaks form. Then add the vanilla bean seeds and mix well.

Place the marshmallow into a piping bag and pipe it into the bottom and sides of the mold. Leave the middle space empty. Place the nutella into a piping bag and pipe it into the center. Pipe some more marshmallow on top to seal the nutella in.

Spread some more chocolate on top to seal everything in. Leave the mold at room temperature overnight, for the marshmallow to set. The chocolate will still set, it will just take longer and overnight is plenty of time!

Unmold and enjoy!