Melt chocolate chips in microwave safe bowl for 30 seconds. Stir. Continue to microwave in 15-second intervals until chocolate chips are melted and smooth. DO NOT overheat the chocolate. Add a spoonful of chocolate into 6 chocolate mold cavities. Smooth chocolate up the sides of each mold with a spoon. Add more chocolate as necessary to coat the inside of each mold.Let the chocolate sit for a few minutes. Check to see if there are any areas that need to be covered again, then smooth out the sides with a spoon. This will help ensure that the sides and center of the mold are evenly coated with chocolate.There will be a little extra chocolate leftover in the bowl. Save this to patch any weak areas or seal the middle seam after the chocolate hardens. Refrigerate chocolate for at least 30 minutes or until completely set.Gently remove from the mold. Fill 3 halve-spheres with 1 tablespoon of cocoa mix and 1 tablespoon of mini marshmallows.
You will need a hot bowl or plate. Press one of the empty chocolate cups against the warm plate to slightly melt the rim.
Place the empty chocolate cup over one of the filled ones. Work quickly and try not to handle the chocolate too much. The warmth of your hands will leave fingerprints and can soften the chocolate. If you notice this happening just pop the chocolates back into the refrigerator for a few minutes.
Run a hot spoon along the seam where the two chocolate cups meet to slightly melt the chocolate and seal the seam. If you have any gaps you can also pipe some melted chocolate over the seam and it will also seal it nice and tight.
Melt white chocolate chips and place in a plastic baggie. Cut the corner and drizzle over hot chocolate bombs (optional). If you'd like to add any decorations (like sprinkles), you can do that at this time while the white chocolate is still melted. Refrigerate chocolate bombs for 30 minutes.
To make a cup of hot chocolate, place one hot chocolate bomb in a mug. Pour 1 1/2 cups of hot milk over bomb. Stir. For an even richer cup of hot chocolate, add a splash of heavy cream.