Melt the white chocolate bark according to the package directions.

Add 2-3 tablespoons of melted white chocolate to each hole in the heart-shaped mold. Use a spoon or culinary brush to make sure the chocolate covers both sides evenly and thoroughly.

Place the chocolate in the fridge until it has hardened completely-- about 5 minutes.

Remove the chocolate shells from the mold and fill one side with two tablespoons of hot chocolate powder and as many marshmallows as you would like (and will fit).

Place a nonstick skillet over medium-low heat. Place the rim of an unfilled shell on the plan for 3-5 seconds, or until the edge starts to soften.

Gently push the two shells together to seal. Place the sealed bomb back in the fridge to set for five minutes.

(Optional) Drizzle over the additional melted chocolate and decorate with sprinkles, if desired.

To serve, add one hot chocolate bomb to a large mug. Pour over the hot milk and stir until the bomb has opened and the powder has dissolved.

Serve immediately.