In a microwave safe bowl, melt chocolate on 50% power level for 2 minutes, stopping to stir every 20 seconds until smooth. (See tips for melting chocolate).
Use a spoon or pastry brush to spread melted chocolate into semi-sphere silicone molds (1 1/2 to 2-inches in diameter).
Place chocolate filled molds in the freezer to set for 5 minutes.
Remove molds from freezer and repeat the process. Spread another layer of chocolate inside each semi-sphere, paying close attention to coat the sides and edges of the molds. Freeze for 5 to 10 minutes.
Microwave a plate for 30 seconds until warm. Carefully remove chocolate from the molds (use food safe gloves to avoid finger prints). Place to semi-spheres on the warm plate with the edge side down to melt the edges. Work quickly and fill one half with cocoa mix and mini marshmallows. Place the other half on top and connect the edges where the chocolate has melted. Use fingers to smooth the edges if necessary. Place on a tray to set.
Place one hot chocolate bombs in a mug. Pour warm milk over the hot chocolate bombs and watch the chocolate melt away to release the cocoa and marshmallows. Stir and enjoy!
Chocolate to use: Semisweet, dark or milk chocolate works for this recipe. Make sure the chocolate is in equal sized pieces for even melting.Hot cocoa: 2 to 3 teaspoons fits inside a hot chocolate bomb. Since the hot chocolate bombs have a chocolate mold, the cocoa will be plenty chocolate-y. If you want more chocolate flavor, use two hot chocolate bombs in one mug.Mini marshmallows: I prefer dehydrated mini marshmallows because you can fit more in a hot chocolate bomb. If you use standard mini marshmallows, you can only fit 3 or 4 in each bomb.Store hot chocolate bombs in an airtight container at room temperature for 1 week or in the freezer for 1 month.Recommended tools: 1.5 inch silicone mold or 2 inch silicone mold and food safe gloves