I used bought sweet pastry tartlet shells. These can be raw to be blind baked at home or pre baked in store. Of course you can use your own favourite sweet pastry recipe.
Make your jelly to specifications on the back but use 1/4 of a cup less of hot and cold water. Sit mixed jelly in the fridge and stir every now and then to cool. You're looking for jelly that's cold and just setting around the edge of the jelly mix, thickening but still sort of pourable.
Wash and dry your berries then hull (cut tops off). For the tartlets I used 1 strawberry per tart, half to cut into pieces to pop in the tart case the other half to slice and fan on the top. (6 to chop and 6 to slice)
Pop 1/2 chopped strawberry into the pastry shell, pour over enough jelly to come to the top of the pastry.
Place filled cases onto a flat tray and pop into the fridge until time to serve.
Whip your cream (if need be with a table spoon of icing sugar to sweeten) to soft/firmish peaks and set aside in the fridge until serving time.
When time to serve either dollop or pipe cream onto the jelly tartlet and top with the other half of sliced and fanned strawberry. You can dust with icing sugar if you wish. Keep in the fridge for up to 2 days, I decorate as needed.
I use fresh berries both in and on top of the tartlet. Strawberries, blackberries, raspberries, blue berries, mixed berries.
I've not used frozen berries but if I did I'd watch how the jelly set as I know there is extra liquid in frozen berries though I don't see how they would affect the top in decorating with them.
Sometimes I make my sweet pastry sometimes I buy depends on my time.
Make a large one to cut into wedges instead of individual.