Crumble the biscuits into coarse crumbs into a bowl. Melt the butter in a water bath and pour it over the biscuits. Stir everything well. Pour it into a form with removable walls.
Using your hands or a suitable spatula, press the biscuits to the bottom of the form to obtain a thin layer.
Dissolve the gelatin according to packet directions and leave it to swell.
Then, beat the liquid cream in a deep bowl, add the sugar and sour cream to it and start beating with a mixer. Once your cream is ready, melt the gelatin in a water bath.
Next, pour the gelatin into the bowl with the cream and stir well. Pour over half of this mixture over the biscuit layer and spread it out. To the rest of the cream mixture, add a little bit of the cocoa, just to darken it slightly.
Stir well and pour it over the other cream. Smooth it out and sprinkle cocoa with a strainer. Optionally, sprinkle chocolate sprinkles as well.
Cover with foil but don't let it touch the cream and put it in the fridge for at least 1 hour. Then take the parfait out and remove the walls of the form. You can serve right away or leave it to cool a little more.