Prep your tools. Make sure molds are clean and completely dry. Any moisture can seize chocolate. Set a baking sheet nearby to support the molds and clear space in the fridge if needed.

Chop the chocolate. Finely chop it so it melts evenly. Smaller pieces reduce hot spots and help with smooth tempering.

Melt and temper the chocolate. Microwave 2/3 of the chocolate in 15–20 second bursts, stirring between each, until just melted and around 105–110°F for dark (95–100°F for milk/white). Stir in the remaining 1/3 finely chopped chocolate (seeding) until smooth and glossy. Aim for 88–90°F for dark or 84–86°F for milk/white before using. This step gives you shiny, snappy shells.

Coat the molds (first layer). Spoon 1–2 teaspoons of tempered chocolate into each cavity. Brush or swirl to cover the whole surface, pushing chocolate up to the rim. Flip the mold over the bowl to let excess drip back. Scrape the top clean.

Chill briefly. Set the mold on a baking sheet and refrigerate for 5–7 minutes, or until set but not brittle. You want a clean snap, not frost.

Add a second layer. Repeat with another thin coat to reinforce edges and prevent leaks. Focus extra chocolate around the rims. Chill again for 5 minutes until fully set.

Unmold the shells. Gently peel the silicone away from the edges and pop the shells out. Handle with gloves or clean, dry hands to avoid fingerprints.

Warm and level the rims. Heat a plate or skillet until warm (not scorching). Press the rim of each shell briefly to melt and level the edge. This ensures a clean seal later.

Fill the bottoms. In half the shells, add about 1 tablespoon hot cocoa mix, a small handful of mini marshmallows, and any extras. Don’t overfill or the seam won’t close.

Seal the bombs. Warm the rim of an empty shell on the plate for a second, then place it on a filled shell to create a sphere. Hold gently until the seam sets. If gaps remain, pipe or dab a little melted chocolate along the seam and smooth with your finger or spatula.

Decorate. Drizzle with contrasting melted chocolate and add sprinkles, crushed peppermint, or cocoa powder. Let set at room temperature until firm.

Serve. Place a bomb in a large mug. Pour 8–10 ounces of hot milk over the top. Stir well as the shell melts and marshmallows pop out. Taste and adjust sweetness with more milk if needed.