Add 4 cups blackberries to a 9x9 baking dish. Zest the lemon and set the zest aside. Squeeze about 1 tablespoon lemon juice over the blackberries.
In a small bowl, combine 1 cup flour, 1 cup sugar, 1 large egg, and zest from one lemon. The mixture will be crumbly. Cover the berries with the mixture.
Slice 6 tablespoons butter into thin slices and spread as evenly as possible on top of cobbler mixture.
Bake in preheated oven for 45-50 minutes until golden brown.