Preheat the oven to 375 degrees. Line muffin tins with paper liners.
Sift the flour, sugar, baking powder, baking soda, and salt into a large bowl and blend with your hands. In a seperate bowl, whisk together the buttermilk, butter, lemon zest, and eggs. Stir the buttermilk mixture into the flour mixture with a fork, mixing just until blended. Fold the blueberries into the batter. Don't overmix! With a standard (2 1/4-inch) ice-cream scoop or large spoon, scoop the batter into the prepared cups, filling them almost full.
For the topping, place all the ingredients in the bowl of a food preocessor fitted with the steel blade and pulse until the butter is in very small pieces. Pour into a bowl and rub with your fingers until crumbly. Spoon about 1 tablespoon of the streusel on top of each muffin. Bake the muffins for 20 to 25 minutes, until golden brown.
Note: Wash blueberries in a strainer under running water and pick out any stems and leaves.