Finely chop the dates. Add to a saucepan with the boiling water and the vanilla extract. Bring to the boil and simmer for 2-3 minutes, then remove from the heat. Allow to cool for around 10 minutes before you make the cake batter.
Preheat the oven to 180°C/ Fan 160C / Gas Mark 4. Add the butter and sugars to a mixing bowl and beat with an electric whisk for 1-2 minutes.
Add the eggs then beat again until combined. Sift in the flour and bicarbonate of soda and beat again for another minute. Add the dates and fold in using a spatula until fully combined.
Grease the dish with the extra butter and pour in the batter. Bake in the centre of the oven for 30-35 minutes until the cake starts to come away from the sides of the dish. Set aside to cool slightly while you make the sauce.
For the sauce:
Melt the butter, vanilla essence and sugar in a large pan over a low heat, stirring regularly. Once the sugar has dissolved add the cream, bring to the boil and simmer for 1-2 minutes.
Pour the sauce over the warm cake and serve straight away. Can also be served with extra custard or ice-cream too.