In a heatproof bowl, melt the dark chocolate chips using a microwave in 30-second intervals or over a double boiler until smooth. Stir well between intervals to ensure even melting.
Once melted, use a spoon to coat the insides of each cavity in a silicone mold. Ensure a thick layer to avoid breaking when unmolding. Place the coated mold in the fridge for about 10-15 minutes to set.
After the first layer is set, repeat the coating process to create a thicker shell. Place back in the fridge for another 10-15 minutes until fully hardened.
Gently pop the chocolate shells out of the silicone mold. Take care to avoid breaking them.
In half of the chocolate shells, spoon about 1 tablespoon of cocoa powder, add a layer of mini marshmallows, and drizzle with caramel sauce. Top with a pinch of sea salt.
Heat the rim of the empty half-shells briefly on a warm plate, then gently press them onto the filled half to seal. Use extra melted chocolate if necessary to ensure they are well sealed.
Drizzle any remaining caramel sauce over the completed bombs and sprinkle with a bit more sea salt for a decorative touch.
To use, place a hot chocolate bomb in a mug and pour steaming milk over it. Watch it melt and stir to combine, then enjoy your delicious salted caramel hot chocolate!