Place the defrosted berries and their juices in a medium mixing bowl. Sprinkle over the granulated sweetener and stir gently to combine. Only stir once to avoid breaking up the fruit. Set aside for 10 minutes while the sweetener dissolves.
Line 4 x 300ml ramekin dishes with clingfilm, allowing it to overlap the rim of the dishes by about 5cm.
Lay the slices of bread out on a chopping board. Using an 8cm plain round cutter, cut out 8 discs of bread from one corner of each slice.
Take 4 of the discs of bread and dip one side in the sweetened fruit juice in the bowl. Place one disc, dipped side down, in the bottom of each ramekin dish, reserving the other 4 for later.
Cut the remaining bread into rectangles approx 5cm x 4cm. You will find you will have to cut some a little narrower. Dip one side of each rectangle in the sweetened fruit juice in the bowl and use these to line the sides of each dish, placing the dipped side against the side of the dish. It doesn't matter if the pieces of bread are uneven shapes, just make sure they cover the sides and up to the rim of the dishes.
Reserve a little fruit juice for dipping the remaining 4 discs of bread, then spoon the berries and their juices into the 4 bread lined dishes right up to the top. Press the berries down lightly with the back of a dessert spoon.
Take the 4 remaining discs of bread, and dip one side of each in the reserved fruit juice. Place on top of the fruit, the dipped side facing up. If you have any juice left, drizzle this over the puddings.
Make sure that the clingfilm is hanging down around the edges of each dish, then cover the tops with another piece of clingfilm and fold down.
Place the dishes on a tray and place something heavy, such as a tin of food or a filled jam jar on top of each. Place the tray and weighted dishes in the fridge for 4 hours.
To remove the puddings from the dishes: Take the weights off the top of each pudding. Remove the clingfilm from the tops of each pudding and discard.
Place a small serving plate upside down on top of each pudding. Hold the pudding and plate together and turn over so that the pudding is now sitting on the plate.
Carefully remove the ramekin dish from each pudding, using the overlapping clingfilm lining to help you. Once the ramekin dishes have been removed, peel the clingfilm lining away from the puddings and discard.
Serve with a few extra summer berries and a squirt of aerosol cream if you wish.