Set a large plate in the freezer.
In a large glass measuring bowl, add the chocolate wafers. Heat wafers in the microwave for 15 second intervals, gently stirring in between each interval, about 1-½ minutes total or until chocolate is smooth and fully melted.
Using a spoon, add chocolate to each egg cavity and coat the cavity with a thin coat of chocolate. Place chocolate coated mold into the freezer for 5 minutes. Repeat these steps 2 to 3 more times until the egg is coated with a sturdy layer of chocolate (about ¼-inch thick). Add the remaining chocolate to a plastic baggie. Set aside.
Add 1 tablespoon cocoa to each egg cavity. Top with 3 marshmallows, if using, being careful not to fill the egg over the top of the mold. Gently press marshmallows into the cocoa.
Push the remaining chocolate in the plastic bag down into one corner to make a cone shape. Using a scissors, snip off a small pointed corner of the bag. Drizzle the melted chocolate over the top of the filled egg until the egg cavity is full, but not overflowing. Using the back of a spoon, smooth the chocolate filling. Place the eggs molds in the freezer for 10 minutes or until firm.
Remove the plate and egg mold from the freezer. Turn the mold upside down and carefully push the eggs onto the cold plate. Drizzle the remaining melted chocolate over the top of eggs. Sprinkle with the decorating sprinkles.
To serve, steam 1 cup of milk per serving. Place the chocolate bomb into the bottom of a mug and pour the milk over the top. Stir well.