Step 1: Preheat your oven to 350°F (175°C) and grease a 9-inch springform pan or line it with parchment paper.
Step 2: In a small bowl, combine the chopped dates, boiling water, orange juice, and baking soda. Stir and let soak for 15 minutes.
Step 3: In a large mixing bowl, cream the softened butter and brown sugar together until light and fluffy.
Step 4: Add the eggs one at a time, beating well after each addition, then stir in the orange zest and vanilla extract.
Step 5: Sift the flour, baking powder, and salt into the wet ingredients. Fold gently until just combined.
Step 6: Stir in the soaked date mixture, including any remaining liquid, until the batter is uniform.
Step 7: Prepare the crumble by rubbing the cold butter into the flour, sugar, and pistachios until it forms small clumps.
Step 8: Pour the batter into the prepared pan and sprinkle the pistachio crumble evenly over the top.
Step 9: Bake for 40-45 minutes or until a skewer inserted into the center comes out clean. Let cool in the pan for 10 minutes before transferring to a wire rack.