Sift the flour, baking powder, and half of the allspice into a large mixing bowl.
Add 6 tbsps of the ground brown sugar and mix.
In a separate bowl, whisk the egg whites together.
Add the butter, yogurt, and vanilla extract and mix well.
Next, stir in the fresh blueberries until thoroughly mixed.
Then, add the fruit mixture to the flour mixture, then gently stir together until just combined. Do not over-stir the batter – it is fine for it to be a little lumpy.
Divide the muffin batter evenly among the 12 cups among the muffin liners (they should be about two-thirds full).
Transfer to a preheated oven at 375F/190C, and bake for about 25 minutes until risen and golden.
Remove the muffins from the oven and serve warm or place them on a wire rack and let cool.