Preheat oven to 190C.
Using plenty of flour roll the cold pastry to a thickness of 2mm. Cut the pastry with a 7.5cm round cutter and use the disks of pastry to line a standard flat based bun tray.
Cut the rhubarb into slices 3mm thick and arrange on each disk of pastry. Place a rounded teaspoon of caster sugar on top of the rhubarb in each tartlet. Bake the tartlets for 15-20 minutes or until the sugar begins to caramelise and the pastry is golden brown. Remove the tartlets from the bun tray while still hot - use a palette knife for this - and place on parchment paper which has been sprinkled with caster sugar.
These tartlets are best served warm.
Open Apple Tartlets: Replace the rhubarb with thinly sliced eating apple.
Green Gooseberry Tartlets (topped and tailed): Replace the rhubarb with halved green gooseberries cut side up.
Sieve the flour into the bowl of an electric food mixer. Cut the butter into small cubes and rub into the flour using the paddle attachment until the mixture forms a coarse texture. DO NOT over mix, if you do the mixture will form a shortbread like ball! Pour the cold cream into the coarse mixture and mix on a low speed until a smooth pastry forms. Wrap the pastry in parchment paper and chill overnight.
Always roll cream pastry straight from the fridge. If the pastry comes to room temperature it will be too soft to handle!