Preheat oven to 350°F and grease a 9x5-inch loaf pan.
Sprinkle baking soda over dates; pour boiling water over them. Rest 15 minutes.
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 flour until just moist; do not 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.