In a pot or pan, combine the tamarind paste, dates, and 2 ¼ cups water. Bring to a boil, reduce to a simmer, and cook, stirring a few times, until the dates are soft, 8 to 9 minutes. Add the brown sugar and cook, stirring to dissolve the sugar, until the mixture starts to thicken, 1 to 2 minutes. Add the cumin, coriander, ginger and chile, if using. Simmer to incorporate the flavors, 1 to 2 minutes. Remove from the heat, season to taste with salt, and let cool slightly. Transfer the mixture to a blender and puree. Strain to remove any tamarind seeds.

Transfer to a bowl and serve at once, or cover and refrigerate for up to 1 week. Rewarm before serving.