Chop the semi-sweet chocolate into fine pieces for even melting.

Place 5 ounces of chopped chocolate in a microwave-safe bowl. Melt in 15-second intervals, stirring in between, until smooth. Use a thermometer to ensure temperature is between 100-113°F, not exceeding 120°F.

Add remaining chocolate pieces and stir until mostly melted. Cool the mixture to about 85°F.

Microwave the chocolate again for 15 seconds to reheat to 90°F for moldability.

Use a basting brush or spoon to coat the inside of each silicone sphere with melted chocolate, applying two thin coats.

Scrape excess chocolate from molds and refrigerate for 3-5 minutes until set.

Gently pop the chocolate spheres out of the molds.

Fill one half of each sphere with 1.5 teaspoons of hot cocoa mix and some mini marshmallows.

Heat a plate in the microwave for 1 minute. Place the open side of each sphere onto the plate for a second to melt the rim, then quickly seal the sphere halves together.

Melt white chocolate in a piping bag or Ziploc, then drizzle over the assembled hot chocolate bombs as decoration.