Add the dates and boiling water to a bowl and leave to sit for about 15 minutes. After 15 minutes add to a food processor or blender and blitz until smooth.
Pre heat the oven to 180C. Beat the butter and sugar in a large bowl until creamy and then add the eggs one at a time, continuing to beat until combined. Add the vanilla and black treacle and beat again.
Fold in the flour, bicarbonate of soda, salt and the date mixture until combined. Fold in the milk a little at a time (don't worry if the mixture does curdle slightly, this is because of the dairy free milk and the date mixture mixing together).
Transfer the mixture to the baking dish and bake for 35-40 minutes, until a skewer comes out clean.