In a saucepan, bring all the ingredients to a boil while stirring. Let the sauce reduce for 5 minutes. Set aside.
With the rack in the middle position, preheat the oven to 350°F (180°C).
In a small saucepan, bring the water and dates to a boil. Stir in 1/8 tsp of the baking soda. Remove from the heat and let cool.
In a bowl, combine the flour and the remaining baking soda. Set aside.
In another bowl, cream the butter, sugar and vanilla with an electric mixer. Add the egg and beat until smooth. At low speed, stir in the dry ingredients alternately with the milk and date mixture.
Spoon the batter into an 8-cup (2 litre), 8-inch (20 cm) soufflé dish. Slowly pour the toffee sauce over the batter. Place the dish on a baking sheet.
Bake for 1 hour or until a toothpick inserted into the centre of the cake comes out clean. Let cool.
Serve warm or freeze. If frozen, place the dish in a large pot and add water to reach halfway up the dish. Over medium heat, let the water simmer, covered, for 1 hour and 30 minutes or until the cake is heated through and the toffee sauce is hot.