Preheat the oven to 190°C.
Line a 20cm square cake tin with baking parchment.
Simmer prunes and water in a saucepan for 2 to 3 minutes until boiling.
Stir vanilla extract into the prune mixture.
Blend the mixture with a stick blender until it becomes thick and soupy.
Beat butter and sugar together, then mix in golden syrup, treacle, and flour.
Incorporate eggs into the butter mixture one by one while stirring well.
Mix bicarbonate of soda into the prunes and combine with the flour mixture.
Pour the batter into the prepared cake tin.
Bake for 1 to 1.5 hours until the sponge is well-risen.
Gently heat double cream in a saucepan.
Whisk in sugar and butter until completely dissolved.
Whisk in the golden syrup and black treacle.
Serve the hot pudding topped with sauce and ice cream.