Bake the pastry dough
Unroll the dough, scatter over the sugar and very lightly roll with a rolling pin. Cut the dough lengthwise into 6 strips, cut crosswise into 4 equal-sized rectangles, place on the oven tray with the baking paper and very firmly prick with a fork.
Bake for approx. 11 mins. in the bottom half of an oven preheated to 220°C. Remove from the oven, allow to cool on a cooling rack.
Place the caramels and milk in a small pan and melt over a low heat, stirring. Divide the caramel onto 8 dough pieces, scatter over the Fleur de Sel, leave the lid to dry.
Beat the cream until stiff. Stir the mousse powder into the water and carefully fold in the cream. Spoon the mixture into a piping bag with a serrated nozzle (approx. 14 mm diameter) and pipe onto the remaining pieces of dough. Place 2 pieces of dough on top of each other. Place the dough lids on top, press down lightly, chill for approx. 30 mins.