Sieve the cocoa powder, full cream milk powder, and powdered sugar. Combine until all the ingredients are mixed.
Heat a saucepan half filled with water over medium heat. Bring the water to simmer.
Place about ⅔ of the dark chocolate into a heatproof mixing bowl. With heat turn off, double boiler the chocolate until it reaches 100°F. The temperature should not exceed 115°F.
After the chocolate melted and reached 100°F, remove it from the saucepan and cool it down with the rest of the chocolate chips that have not been melted. Keep stirring until it reaches 84°F.
It will take a while to reach 84°F, if you do not have patience, use an ice pack by sticking it outside the bowl. Once it reached 84°F, double boiler it again with the heat turned off until it reaches 89°F.
Brush 2-inch of six silicon dome molds with gold powder, then add in about 1 tbsp melted chocolate and use a brush to spread the chocolate. Make sure the entire inside of each mold is evenly coated.
To make a perfect bomb, turn it upside down onto parchment paper and refrigerate for 15 minutes. Once set, carefully remove the chocolate from the mold.
Add 1 ½ tbsp cocoa milk powder, 1 tbsp mini marshmallow, and ½ tsp gold sanding sugar. Spread some melted chocolate on the rims of the chocolate ball then seal it with half of an empty chocolate ball.
To decorate the chocolate bombs, drizzle with some melted chocolate then sprinkle it with gold sanding sugar.
To make hot chocolate, heat 1 cup of milk until almost boiled, pour it into a mug, and gently place the chocolate bomb. Stir once the chocolate bomb explode.
Enjoy!