Preheat the oven to 180°C (350°F) and grease the baking dish.
In a small bowl, combine the chopped dates and boiling water. Stir in the baking soda and let it cool for about 10 minutes.
In a mixing bowl, cream the softened butter and brown sugar until light and fluffy.
Add the eggs, one at a time, beating well after each addition.
Mix in the cooled date mixture until combined.
Sift together the flour, baking powder, and salt in another bowl. Gradually fold this dry mixture into the wet ingredients using a rubber spatula until just combined.
Pour the batter into the prepared baking dish and smooth the top.
Bake in the preheated oven for 30-35 minutes, or until a toothpick inserted in the center comes out clean.
While the pudding is baking, prepare the toffee sauce: In a saucepan, combine the heavy cream, brown sugar, and vanilla extract. Cook over medium heat until the sugar dissolves and the sauce thickens, about 5-7 minutes.
Once the pudding is finished baking, remove it from the oven and let it cool for a few minutes before serving.
Cut the pudding into squares, serve warm with generous amounts of toffee sauce drizzled on top.