Preheat oven to 400 F.

In a medium bowl, sift together the flour, brown sugar, baking powder, baking soda, salt.

In a large bowl, beat together the eggs, butter, yogurt, lemon juice, and vanilla just until smooth.

Pour the flour mixture into the butter mixture. Mix until just combined.

Fold in the blackberries and lemon zest carefully until evenly distributed.

In a well greased muffin pan, scoop the mixture evenly, filling to the top.

Place muffins in the oven for 15-18 minutes, until a toothpick can be inserted and comes out clean.

Remove muffins from oven and let cool.

Mix together the powdered sugar and lemon juice until smooth.

Once the muffins are cooled, drizzle the glaze over each muffin.