Preheat the oven to 375°F (190°C). Butter a 12-cup muffin tin.
Place the dates in a shallow bowl (in a single layer if possible), pour the boiling water over them, and let soak for 15 minutes.
Transfer the dates and soaking liquid to a food processor and puree until almost smooth save for a few pea-sized fruit pieces. Set aside to cool slightly. Meanwhile, in a medium bowl, combine the flour, baking powder, and salt.
In the bowl of an electric mixer, beat the butter and brown sugar. With the motor running, mix in the eggs, 1 at a time. Add the vanilla. Add half the flour mixture and mix until moistened. Follow with the date puree and, when thoroughly combined, mix in the remaining flour mixture. Scrape down the sides of the bowl and give a final stir with a spatula to make sure all the ingredients are thoroughly combined.
Divide the batter among the muffin cups. Top with the streusel and press down gently to adhere. Bake for 20 to 25 minutes.