Coarsely chop the dates and place them in a bowl. Pour the boiling water over them and stir in the baking soda. Let the dates soak until cooled down. Using an immersion blender or placing them in a regular blender, puree the dates to make a chunky-smooth mixture (don't puree it completely smooth).
Preheat the oven to 350 degrees F.
In a large mixing bowl cream the brown sugar and butter until smooth and pale. Beat in the eggs and oil. Add the black treacle and vanilla extract and beat until combined.
In a small bowl, stir together the flour, baking powder and salt. Gradually beat in the flour mixture into the wet mixture just until combined. Add the chunky date puree and beat just until combined.
Generously butter a jumbo/king-sized muffin pan (holds roughly 1 cup). Spoon the batter in until about 2/3 full. Bake the cakes on the middle rack for about 25 minutes (about 40 minutes if using the 8x8 inch cake pan - SEE NOTE) or until a toothpick inserted into the center comes out clean. Let the cakes cool for a few minutes in the tins and then remove and place them on wire rack.
Optional: For a more caramelized and moist cake, add about 2 teaspoons of brown sugar and 1/4 tablespoon butter in the bottom of each muffin mold before spooning in the batter (see blog post pictures). We highly recommend it!
*Alternatively, instead of individual puddings you can also bake it in a 8x8 inch (or slightly bigger) buttered cake pan. Pour some of the toffee sauce over the cooled cake (broil it briefly in the oven until bubbly if desired), cut and serve with extra toffee sauce on the side.*This cake freezes well. Wrap it well and freeze for up to 2 months, then thaw, heat and serve with warm toffee sauce. The toffee sauce can also be made weeks in advance. That way you can always have some Sticky Toffee Pudding on hand whenever you have guests or have a sudden craving!