Green apple mousse:
Soak the gelatin in some water to dissolve.
Peel the apple, get rid of seeds, cut into squares and toss in the blender together with lemon juice, rum, and sugar. Heat the mixture on about 60C and add the swollen gelatin. Cool them down to 28C and mix with whipped crème.
Immediately apply the mousse on apple pieces and evenly divide. Top them with the first chocolate biscuit and press it.