Combine the flour, baking soda, baking powder, and salt in a mixing bowl then mix well.
Cream the butter in a separate mixing bowl and add the sugar (white and brown) while continuously mixing until texture becomes fluffy.
Beat-in the eggs on the mixing bowl with butter and sugar then continue mixing until everything is well distributed.
Gradually add the flour-baking soda-baking powder-salt mixture while continuously mixing.
Put-in the dates and walnuts then mix until well distributed.
Preheat oven to 350 F.
Grease the baking pan and pour-in the batter.
Bake for 10 minutes then pull down the temperature to 300 and continue baking for 35 minutes or until done (you may use the toothpick test).
Remove from the oven and allow to cool down.
Slice and wrap individually if desired.