Line a loaf pan with parchment paper and set aside.
In a saucepan mix together the chopped dates, water and baking soda. Then over low-medium heat, bring the mixture to a boil, then add the tablespoon of butter. Let simmer for about 5 minutes, or until the dates are soft and mushy. Set aside to cool.
In a separate bowl sift together the flour and baking powder.
Using a mixer cream together the egg, brown sugar and vanilla until smooth.
Once the date mixture is cooled, add it to the egg mixture and combine.
Stir in the flour mix.
Pour the batter into your prepared loaf pan.
Bake for 1 hour and 15 minutes, or until a toothpick inserted into the centre of the cake comes out clean.