Brush a tart mould with a lifting base and smooth rim (approx. 23 cm Ø; alternatively springform pan, 24 cm Ø) well with oil. Put the biscuits in a freezer bag, close the bag and crumble the biscuits finely with a dough roller.
Heat the butter, mix it with the cookie crumbs and put it into the mould. Press to even base and raise one rim. Chill for at least 1 hour.
Break the chocolate into pieces and melt in a hot water bath. Let it cool down a little. Whip cream and sour cream separately with 1 packet each of vanilla sugar until stiff. Mix cream and sour cream. Peel bananas, cut into slices and mix with lemon juice.
Carefully remove the biscuit base from the mould and place it on a cake plate. Cover the base with banana slices. Spread the caramel spread in blobs on top. Spread sour cream on top.
Spread warm chocolate in several portions in blobs on the cream and spread it quickly in a circle with the back of a spoon. Chill for about 30 minutes, then serve immediately.