Cut the chocolate chiffon sponge and peanut crispy base into 4-in/10-cm rounds. Brush the sponge with the banana syrup to moisten. Press together 1 sponge round and 1 crispy base so they stick.
Place dome-shaped flexible silicone molds face down on a sheet pan. Using a pastry bag with a 1-in/3-cm opening, pipe the chocolate mousse three-quarters of the way up t