In medium bowl, toss and stir together the blackberries, lemon zest, and half the sugar. Gently mashing them a bit to get their juices going. Let stand about 15-20 minutes or until fruit syrup starts to form.
In the meantime pre heat oven to 375°F.
In large bowl, whisk together flour, remaining sugar, cinnamon, baking powder, salt, vanilla and milk. Stir in melted butter until combined.
Pour batter into an ungreased 8-inch square pan Or a skillet.
Spoon blackberry mixture over batter.
Bake 45 minutes or until batter rises and forms a golden crust. (depending on the oven it could take up to 55 minutes - I usually start checking at the 30 min mark) Let stand a few minutes out of the oven then serve warm with ice cream or vanilla whip cream.
