Put 1 sachet of sugar and frozen berries into a food processor and process until coarse or smooth, depending on your liking. Add a couple of spoonful of water (or liqueur), and whizz until you get a thick, mixture. Set aside.
Pour the cream and the other sachet of vanilla sugar into a medium sized bowl and whisk or beat with an electric mixer until you get a thick but fluffy cream.
Crush your chosen biscuits to breadcrumbs.
Get 4-6 small glasses or bowls ready. Spoon a heaped Tbsp of the crumble into the bottom of each vessel, then spread some fruit purée over it, followed by some cream mixture. Repeat the layers once more.
Finally add a few frozen berries to garnish and finish off with some biscuits sprinkled on top.
Cover the pots and keep them in the fridge until you're ready to serve.