A hot cocoa bomb is a hollow chocolate sphere with cocoa mix and marshmallows sealed inside. Pour steaming milk over one in a mug and the shell gives way, the marshmallows float up, and you have hot chocolate. Adrianna of Sugarologie makes nine of them here, three each from milk, dark and white chocolate, and she films the two parts most tutorials rush past: how thick the shell has to be, and how to weld the halves together without a gap.
Two decisions come before any melting. The mold has to be thin, floppy silicone you can turn inside out, because a rigid one cracks the dome as you pull it free. And use melting wafers or a real chocolate bar, never chocolate chips, which are built to hold their shape in a cookie and set dull and streaky in a mold. Wafers are the easy road because they need no tempering. For real chocolate, Adrianna tempers in the microwave by melting 75 percent of it and stirring the reserved 25 percent back in.
Budget about 30 minutes of hands-on work and two short trips to the fridge. One 8 ounce bag of wafers fills six cavities, which is three finished bombs.
The drink is the easy half. See how to make hot chocolate for the from-scratch version, and finish a mug with homemade whipped cream. If you are filling a holiday tin, peppermint bark and fudge come out of the same bag of chocolate.
How thick the shell needs to be
Two millimetres, roughly the thickness of a coin. Thinner and the dome cracks as you peel the mold back, which is the failure that ends most first attempts. Thicker and the shell survives handling but takes so long to give way in the mug that the marshmallows are still trapped when the milk has cooled.
Getting there takes two coats. Spoon chocolate in, brush it up the walls, chill for five minutes, then brush a second coat over the first paying attention to the rim. The rim is always the thinnest part and it is the part you handle.
Sealing the halves without a gap
Warm a plate or the base of a pan, press the cut edge of each half against it for two seconds to melt it flat, then bring the two together and hold. The melted rims fuse as they set. Piping chocolate into the seam works too but leaves a visible ridge.
Do not fill the shells to the brim. Cocoa powder sitting on the rim stops the chocolate bonding, and the bomb splits in the box. Leave a clear quarter inch.
What goes inside
Two tablespoons of cocoa mix and a small handful of mini marshmallows per bomb is the standard fill. Beyond that, crushed candy cane for peppermint, a pinch of cayenne and cinnamon for Mexican hot chocolate, instant espresso for a mocha, or freeze dried raspberries. Use mini marshmallows only, since regular ones will not fit through the opening without crushing the shell.
Storing them and giving them away
Kept cool and dry in a sealed box, they last about two weeks before the cocoa powder starts drawing moisture through the chocolate and the inside goes clumpy. Do not refrigerate finished bombs: condensation forms on the shell as they warm back up and leaves a dull, sticky bloom.
For gifting, sit each one in a cupcake liner inside a clear favour box, or wrap in cellophane and tie at the top. Add a tag saying to pour 8 to 10 ounces of hot milk over it and stir, because the first thing anyone asks is how much milk.