Step 1: Preheat your oven to 180°C (350°F) and grease a 9-inch square baking pan or a similar-sized cake tin.
Step 2: Place the chopped dates and baking soda in a bowl, then pour the boiling water over them. Let them sit for 15 minutes to soften the dates into a paste-like consistency.
Step 3: In a large mixing bowl, cream together the softened butter and dark brown sugar until light and fluffy.
Step 4: Beat in the eggs one at a time, followed by the vanilla extract, ensuring each is well incorporated before adding the next.
Step 5: Gently fold in the flour and baking powder using a spatula, being careful not to overmix.
Step 6: Stir in the soaked date mixture (including the water) and the toasted walnuts until just combined.
Step 7: Pour the batter into the prepared pan and bake for 40-45 minutes, or until a skewer inserted into the center comes out clean.
Step 8: While the cake is baking, prepare the sauce by melting the butter, light brown sugar, and orange zest in a saucepan over medium heat.
Step 9: Once the sugar has dissolved, stir in the orange juice and heavy cream. Bring to a gentle simmer for 3-5 minutes until the sauce thickens and becomes glossy.
Step 10: Once the cake is out of the oven, prick it all over with a fork and pour half of the warm orange sauce over the top. Let it soak in for 10 minutes before slicing.
Step 11: Serve warm with the remaining orange sauce drizzled over each individual slice.