Preheat oven to 350 degrees.
In a small bowl, combine the blackberries, 2 Tbsp. granulated sugar, lemon juice and 1 tsp. vanilla extract. Set aside.
Place butter in a 2 quart baking dish and place the dish in the oven to melt the butter.
Meanwhile, in a medium bowl, combine the flour, 3/4 cup granulated sugar, and baking powder.
In a small bowl, combine the milk and vanilla.
Stir the milk mixture into the flour mixture just until combined.
When the butter is melted, remove the pan from the oven. Pour the batter over the butter. The melted butter will spill up around the edges – don’t stir it in.
Sprinkle the blackberries evenly over the top and gently press the berries into the batter.
Bake for 40 minutes. Sprinkle the remaining sugar on top and continue baking 5 minutes more or until the buckle has turned a beautiful golden brown.