Crumble the cookies. Melt the butter and chocolate in a water bath, then combine with the cookie bits and mix well. Place the mix in a previously buttered tart tin, firmly pressing it in, then refrigerate.
Warm up all the filling ingredients in a water bath, mix well, allow to cool for a moment, then pour into the pastry shell and wait until it fully cools down; refrigerate.
Heat the water and sugar in a deep pan (or pot), slice the orange and add the slices to the mix. Boil approx. 40 min (watch it continuously to make sure it does not scorch).