Remove the stones from your dates, and chop as finely as possible.
Pour over the boiling water and leave the mixture to sit for 20 minutes or so. If you prefer no lumps, blend the mixture until smooth.
Preheat your oven to 180ºC/160ºC Fan, and get a baking dish ready - I use one that is about 1.5L in size (30x20cm ish)
Add the unsalted butter, sugar, eggs, self raising flour, baking powder, bicarbonate of soda, and the black treacle into a bowl, and beat until combined - beat as little as possible so as not to over beat it.
Add in the date & water mixture, and the milk a little at a time, and mix in until smooth. It'll be a thin mixture, but roll with it!
Pour the mixture into the dish and bake in the oven for 35-40 minutes, or until a skewer comes out clean. Whilst baking, make the sauce!