Step 1: Place the chopped dates in a heatproof bowl and sprinkle with the bicarbonate of soda. Pour the boiling water over them, stir, and let sit for 15 minutes to soften.
Step 2: Preheat your oven to 180°C (350°F) and grease and line a 9×5 inch loaf tin with parchment paper.
Step 3: In a large mixing bowl, cream together the softened butter and brown sugar until light and fluffy.
Step 4: Beat in the egg and vanilla extract until well combined.
Step 5: Sift the flour and baking powder into the bowl. Add the soaked date mixture (including the liquid) and fold gently until just combined.
Step 6: Stir in the chopped walnuts, then pour the batter into the prepared tin. Bake for 50-55 minutes, or until a skewer inserted into the center comes out clean.
Step 7: Allow the cake to cool in the tin for 10 minutes before transferring to a wire rack to cool completely.