Put the tamarind in a medium heat-proof bowl and add the boiling water, pressing down on the tamarind with a spoon so it’s covered with water. Cover with plastic wrap and let sit for at least 1 hour. Massage and squeeze the pulp to soften it, and press through a fine-mesh strainer suspended over a bowl, discarding the solids in the strainer. Measure out 1 cup [240 g] pulp for this recipe. Reserve 2 tbsp of the pulp in a small bowl to prepare the glaze.
Preheat the oven to 350°F [180°C]. Grease an 8½- by 4½-in. [21.5 by 11 cm] loaf pan with butter and line the bottom with parchment paper.
In a large bowl, whisk together the flour, ginger, pepper, baking powder, baking soda, and salt. Put the dates in a small bowl. Add the walnuts and 2 tbsp of the whisked dry ingredients and toss to coat evenly.
Combine the ¾ cup [180 ml] olive oil, 1 cup [240g] tamarind pulp, and jaggery in a blender and pulse on high speed for a few seconds until completely emulsified. Add one egg and pulse for 3 to 4 seconds, until combined. Repeat with the remaining egg.
Make a well in the center of the dry ingredients in the bowl, and pour the egg mixture into the well. Whisk the dry ingredients into the egg mixture and continue whisking until there are no visible flecks of flour. Then fold in the dates and walnuts.
Spoon the batter into the prepared loaf pan. Arrange the walnuts halves in a straight line down the center of the loaf. Bake for 55 to 60 minutes, rotating the pan halfway through baking, until firm to the touch in the center and a skewer comes out clean. Cool in the pan on a wire rack for about 10 minutes, and run a knife around the inside of the pan to release the cake. Remove from the pan and transfer to a wire rack to cool completely.
Add the remaining 1 tsp of olive oil to the small bowl containing the reserved tamarind. Sift in the confectioners’ sugar and whisk until completely smooth. Pour the glaze over the cooled loaf and let it sit for 1 hour to set before serving.