Place the dates in a bowl and pour over 150ml of boiling water. Add the teabag and bicarbonate of soda and leave to soak for ten minutes.
Remove the teabag then add the vanilla extract and mash with a fork.
Preheat the oven to 180oc. Butter a 20cm x 30cm dish or regular pie dish. Line with baking paper.
Beat the butter with the light and dark sugar until smooth then beat in the eggs. Beat in the milk then add the softened dates. Do not worry if the mixture appears to split at this point, it will come back together once the flour is added.
Fold in the sieved flour until combined then pour into the baking tin or dish.
Bake for around 35 minutes until risen and golden.