Preheat oven to 350 degrees F (175 degrees C). Grease an 8-inch square baking dish.

In a small bowl combine the dates and baking soda. Pour enough boiling water over the dates to just cover them.

Beat 1/3 cup of butter with white sugar in a bowl with an electric mixer until light and frothy. Beat in eggs and mix well to combine.

Add flour and date mixture (including water) to the egg mixture and fold to combine. Pour cake batter into the prepared baking dish.

Bake in the preheated oven until a tester comes out clean, 30 to 40 minutes. Let cake cool slightly while you prepare the toffee sauce.

To make the toffee sauce: Combine brown sugar, 1/3 cup butter, and evaporated milk in a small saucepan; cook over medium heat and bring to boil. Turn heat down and simmer for 5 minutes, stirring occasionally. Remove from heat and stir in vanilla. Pour toffee sauce over individual servings of warm cake.