In a microwave-safe bowl, add the milk chocolate chips. Microwave in 30-second intervals, stirring after each interval until the chocolate is completely melted and smooth. Take care not to overheat to prevent burning the chocolate.
Using a silicone sphere mold, pour approximately one tablespoon of the melted milk chocolate into each half of the mold. Use the back of a spoon to evenly cover the inner sides with chocolate. Repeat this process for all molds, then transfer them to the refrigerator for about 10-15 minutes until set.
Once the first layer is solidified, re-melt any remaining milk chocolate if necessary and pour another layer into the molds. Use a spoon to spread it evenly, then return the molds to the refrigerator for another 10-15 minutes to create a sturdy chocolate shell.
Carefully remove the chocolate shells from the molds by gently pressing from the bottom. If any edges are jagged or rough, you can smooth them by briefly running the edges along a heated plate to temper the chocolate.
For half of the chocolate spheres, add a layer of cocoa powder, followed by a few mini marshmallows, and sprinkles if desired. Drizzle a small amount of the melted white chocolate over the filled mixture to help adhere the top shell.
Take the remaining chocolate shell halves and carefully press them onto the filled ones, aligning well. Use the remaining melted white chocolate as a glue to seal the halves together securely. If necessary, hold them briefly until the chocolate begins to set.
For an extra touch, drizzle some melted white chocolate decoratively over the top of the assembled hot chocolate bombs, and finish with a sprinkle of additional sprinkles for a festive presentation.
To enjoy your hot chocolate bomb, place one in a mug and pour hot milk over it. As it melts, watch the magic unfold with marshmallows and chocolate releasing into the milk! Stir well with a spoon to combine all the delicious flavors.