Preheat oven to 350. Put stick of butter in a 9x13 pan i use glass and place in the oven while it preheats allowing butter to brown slightly.
In a bowl whisk together flour, 1 cup of sugar, milk and extract until smooth. In a saucepan gently toss blackberries with the remaining 1/2 cup of sugar and heat for about 5 minutes or until the berries are releasing some juice.
Carefully remove hot 9x13 pan from the oven and carefully pour in the batter and then blackberries. Bake for 45 minutes to 1 hour or until golden brown. Serve with ice cream or whipped cream.