01 - Preheat oven to 350°F. Grease and line an 8-inch square cake pan.
02 - Place chopped dates in a bowl. Pour boiling water over them and stir in baking soda. Allow to rest for 10 minutes.
03 - In a large bowl, cream softened butter with dark brown sugar until light and fluffy.
04 - Beat eggs into the butter mixture one at a time, followed by the vanilla extract.
05 - Gently fold self-raising flour and salt into the wet mixture until just combined.
06 - Slightly mash the soaked dates with their liquid and fold them into the batter.
07 - Transfer batter to the prepared pan and bake for 30 to 35 minutes until a skewer inserted in the center comes out clean.
08 - While the cake bakes, combine dark brown sugar, butter, and heavy cream in a saucepan over medium heat. Stir until the sugar dissolves and the mixture simmers. Cook for 4 to 5 minutes until thickened. Remove from heat and stir in vanilla extract and salt.
09 - When the cake is done, cool for 5 minutes. Prick holes over the surface with a skewer and pour half the toffee sauce over it. Let soak for 10 minutes.
10 - Cut into squares and serve warm, drizzling remaining toffee sauce over each portion.