Start by preparing the cake crust. Place the cookies in a food processor and pulse until finely ground. Melt the butter in the microwave. In a bowl, combine the cookie crumbs, melted butter, and cinnamon. Mix well. Press the mixture firmly into the bottom of a springform pan to form an even crust. Place in the freezer while you prepare the mousse.

Soak the gelatin sheets in a plate of cold water to soften them.

In a saucepan, heat half of the milk with the cinnamon stick, lemon peel, and half of the sugar (reserve the other half for the cream). When it starts to boil, remove from heat and discard the cinnamon stick and lemon peel. Add the softened gelatin sheets and stir until completely dissolved. In the remaining milk, dissolve the 1 1/2 packets of custard mix, then add this to the saucepan. Whisk well until fully combined. Let cool.

In a bowl, whip the heavy cream with an electric mixer. When it is almost whipped, add the reserved sugar and continue beating until stiff peaks form. Once the custard mixture has cooled, gently fold it into the whipped cream a little at a time, using a spatula. Pour the mixture over the cookie crust. Refrigerate for 3 to 4 hours until set.

For the topping: Soak the gelatin sheets in cold water to soften them.

In a saucepan, heat half of the milk with the sugar. In the other half of the milk, dissolve the custard mix. When the milk is hot, remove from heat and add the softened gelatin sheets and the dissolved custard mix. Whisk well until the gelatin is fully dissolved. Let cool.