Preheat oven to 350 degrees. Grease an 8x4 or 9x5-inch loaf pan; set aside.
In a small bowl, combine the dates, baking soda and boiling water. Set aside to cool.
In a large bowl, cream brown sugar with the egg yolk. Add the cooled date mixture; stir to combine. Add salt, flour and pecans.
Whip the egg white to stiff peaks; gently fold into batter. Sprinkle baking powder over the batter and fold to combine. Pour into prepared loaf pan and bake for 30-40 minutes, or until a toothpick inserted into the center comes out clean. Allow to cool in the pan before turning out onto a cooling rack. Prior to serving, dust the top with powdered sugar, if desired.
Will last for several days, well wrapped, at room temperature. (Or freeze for a few months.)