200g (7 ounces) chopped dates (Madjool or a combination of several varieties)
Line the base and sides of a deep, 18cm cake tin with nonstick baking paper, and heat the oven to 180C/350F (160C/325F convection). Put the dates, tamarind paste and water in a pan and bring to a boil. Boil for a minute, remove from the heat, add the butter, and set aside for 10 minutes to cool.
Place the date mixture in a large mixing bowl and add the brown sugar, stir, then beat in the eggs until smooth. Ina separate bowl, mix the flour, baking soda, spices and orange zest together and add to the date mixture until combined. Then, stir in the walnuts.Spoon the mixture into the cake tin and bake for about an hour, or until a skewer poked into the centre comes out clean. Cool for 10 minutes, remove from the pan, and completely cool on a cake rack.