Prepare the salted butter caramel :
Pour the sugar and water into a saucepan. Heat until golden. Stir now and again. Remove from the heat, gradually add the cream then the butter. Mix until the caramel is nice and smooth. Leave to cool.
Empty the jars of rice pudding into a mixing bowl. Keep to the side. Clean out the empty jars.
Crumble the biscuits in another bowl.
Alternate the layers in the jars :
Start with a layer of biscuits, then some salted butter caramel, then cover with a thick layer of rice pudding. Repeat the operation and finish with a layer of salted butter caramel generously sprinkled with crumbled biscuits.
You can replace the Breton shortbread biscuits with crêpe dentelle biscuits.