Temper the White Chocolate:

1. Finely chop the white chocolate.
2. Melt it gently using a double boiler or microwave in 15-20 second intervals, stirring each time to avoid burning. The temperature of the chocolate should reach 40-45°C (104-113°F).
3. Let it cool to 26-27°C (79-81°F), stirring regularly.
4. Then, slightly reheat it to 28-30°C (82-86°F) to properly temper the chocolate. Add a few drops of green gel food coloring and mix until you achieve a uniform green color.

Form the Shells:

1. Using a pastry brush or the back of a spoon, apply the first layer of chocolate into the cavities of a silicone mold. Make sure the layer is even and covers the edges.
2. Let it set at room temperature or in the fridge for 10-15 minutes.
3. Apply a second layer of chocolate to reinforce the shells, then let it set again.

Unmold the Shells:

1. Once the shells are fully set, gently unmold them.
2. Place them on a clean surface and separate them into two groups: one half for the base and the other for the top to close the bombs.

Fill the Shells:

1. Fill each bottom shell with 1 to 2 tablespoons of sweetened cocoa powder, mini marshmallows, and any other fillings you like, such as candies or spices.

Seal the Bombs:

1. Heat a plate in the microwave for 1 minute.
2. Place the edge of the top shell on the warm plate for a few seconds to melt the chocolate edges slightly.
3. Immediately assemble with a filled shell, gently pressing to seal.
4. Smooth the seam with your finger if needed.

Decorate the Bombs:

1. Using a piping bag or spoon, decorate the bombs with melted chocolate.
2. Carefully place a red sugar heart on top and let it fully set before storing or using them.