Coarsely chop 325g of the strawberries; thinly slice the remaining strawberries. Place the chopped strawberries in a food processor or blender; process to a puree. Transfer puree to a medium bowl; stir in the sugar and rosewater.
Prepare whipping cream mix sachets with milk according to package directions. Fold half the strawberry puree into the whipped cream.
Reserve about 20 strawberry slices for garnish. Divide remaining sliced strawberries between six serving glasses. Spoon half of the strawberry cream over strawberries; top with strawberry puree. Spoon the remaining strawberry cream over the puree and top with the reserved sliced strawberries and dried rose petals.