Bring water to a boil in a saucepan, then add chopped dates and baking soda. Reduce heat and simmer for 5 minutes until dates are soft and sticky. Let cool slightly.
In a mixing bowl, cream together softened butter and dark brown sugar until the mixture is light, fluffy, and smells caramelized, about 2-3 minutes.
Add eggs one at a time, beating well after each addition to incorporate air and create a smooth batter. Mix in vanilla extract for warmth and aroma.
Fold the cooled, mashed dates into the wet mixture, combining thoroughly until the batter is rich and sticky.
Sift together self-raising flour and salt, then gently fold into the wet ingredients until just combined. The batter should be thick and glossy.
Pour the batter into an prepared 8-inch baking dish or ramekins, smoothing the surface with a spatula. Bake in a preheated oven at 180°C (350°F) for 25-30 minutes, until edges are golden and a toothpick inserted into the center comes out moist but not wet.
While the pudding bakes, make the toffee sauce by combining heavy cream, black treacle, and a little butter in a saucepan. Bring to a gentle simmer and cook for 2-3 minutes until the sauce is glossy and thickened.
Remove the pudding from the oven and let it rest for 5 minutes. Poke holes all over the top with a skewer and pour warm toffee sauce generously over, allowing it to soak in and caramelize at the edges.
Serve the pudding while warm, with extra sauce drizzled over the crispy edges and a scoop of cream or ice cream if desired. The contrast between crispy caramelized crust and gooey inside makes each bite irresistible.
