Preheat oven to 350°F (175°C) and grease a 9x13 inch baking pan.
Soak chopped dates in boiling water for 15 minutes. Stir in baking soda.
Cream butter and brown sugar until light and fluffy.
Beat in eggs one at a time, then add vanilla extract.
In another bowl, whisk flour, baking powder, salt, cinnamon, and nutmeg.
Fold dry ingredients into wet mixture, alternating with date mixture.
Toss walnuts with 2 tablespoon flour and gently fold into batter.
Spread batter into the pan and bake for 45–50 minutes until a toothpick comes out clean.
Cool in the pan for 15 minutes, then transfer to a wire rack to cool completely.