Preheat oven to 350 degrees F.
Butter an 8 1/2 by 4 1/2-inch loaf pan; set aside. In a small bowl, combine dates and baking soda and pour boiling water over them. Let sit until water is cool.
With a wooden spoon, beat butter and sugar until combined. Add the egg and vanilla and mix well. Add the flour and beat to combine. Stir in the dates with their soaking liquid and walnuts. Scrape into prepared pan. Bake until a cake tester inserted in center comes out clean, about 45 minutes.
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