01 - Preheat oven to 350°F. Grease an 8x12 inch baking dish or 8 ramekins.
02 - Place chopped dates in a bowl. Pour boiling water over and stir in baking soda. Let stand for 10 minutes.
03 - In a large bowl, cream softened butter with dark brown sugar until light and fluffy. Beat in eggs one at a time, then stir in vanilla extract.
04 - Mash softened dates with their liquid into a rough paste, then fold into the butter mixture.
05 - Sift self-raising flour and salt into the mixture. Gently fold to combine without overmixing.
06 - Pour batter into prepared dish or divide among ramekins. Bake for 30 to 35 minutes until risen and a skewer inserted in the center comes out clean.
07 - While sponge bakes, melt butter and dark brown sugar in a saucepan over medium heat. Stir in cream, vanilla, and salt. Simmer for 3 to 4 minutes until slightly thickened.
08 - Once baked, pierce sponge top with a skewer. Pour half the toffee sauce over warm sponge and let soak for 10 minutes.
09 - Drizzle remaining toffee sauce over sponge. Serve warm with a scoop of vanilla ice cream or whipped cream if desired.