Preheat oven to 350°F and grease a 9x5-inch loaf pan.
Place chopped dates in a bowl and sprinkle baking soda over them. Pour boiling water over dates and let stand for 15 minutes to soften.
In a large mixing bowl, cream together butter and sugar until light and fluffy.
Beat in egg and vanilla extract until well combined.
In a separate bowl, whisk together flour and salt.
Add the date mixture to the butter mixture and stir until combined.
Gradually fold in the flour mixture until just moistened, being careful not to overmix.
Gently fold in chopped walnuts.
Pour batter into prepared loaf pan and bake for 55-60 minutes, or until a toothpick inserted in the center comes out clean.
Cool in pan for 10 minutes, then turn out onto a wire rack to cool completely.
Wrap tightly and store at room temperature for up to 5 days, or freeze for up to 3 months.