De-pit the plums. Pop the pitted plums in your blender to chop. Pour finely chopped plums into a saucepan and add water.
On medium to low heat, simmer for about 15 minutes then add in lemon juice and sugar. Boil for 20-25 minutes, stirring to avoid burning. Skim any foam on the top. Jam should deepen in colour and thicken.
When ready, pour into a glass bowl and cool in the
Mix the sugar, flour and butter, rubbing between your hands until crumbly. Add in egg yolk and vanilla.
Mix with your hands to form a dough ball. Cover in cling film and press into a 3cm flat disc. Put in the fridge for 30-45 minutes.
Preheat your oven to 160.C fan. Once chilled, take out and roll flat until about 0.5cm thick.
Using a cookie cutter, cut out 16 biscuits. Cut out the centre of 8 of them using a small cutter.
Place the biscuits on the Pyrex® glass baking dish, (6 should fit on the dish at a time).
Put in the oven for about 14 minutes. Remove and leave to sit for a few minutes before moving to a cooling rack.
Add 1-2 tsp of jam to the centre of the non-holed biscuits and press holed biscuit on top.