A little late, but we didn't get home until after midnight!
I found a recipe on Allrecipes.com and added a couple of things based on some reviews. Here is how I prepared it.
Blackberry Cobbler
1 cup flour
1-1/2 cups sugar, divided
1 tsp. baking powder
1/2 tsp. salt
1/2 tsp. cinnamon
6 TBSP cold butter
1/4 cup boiling water
2 TBSP cornstarch
1/4 cup cold water
1 TBSP fresh squeezed lemon juice
1 tsp. vanilla
1 tsp. orange zest
Preheat oven to 400 degrees F. Wrap a rimmed cookie sheet with foil. Place cast iron skillet on cookie sheet. In a large bowl, mix flour, 1/2 cup sugar, baking powder, salt and cinnamon. Cut in butter with a pastry blender until it is crumbly. Stir in boiling water and stir until it is evenly moistened. Put blackberries in a bowl and sprinkle with a little sugar, the vanilla and the orange zest. In a separate bowl, dissolve the cornstarch in the cold water. Stir in remaining 1 cup sugar and the lemon juice. Stir well to combine and then pour over blackberries; stir to coat all the berries. Pour into the cast iron skillet. Top berries with small spoonfuls of cobbler dough, and spread out dough a little with the back of the spoon. Place in oven and bake for 30 minutes or until golden brown.