Preheat the oven to 375°F. Lightly grease an 8" square pan; a 9" pie pan, or an 8" to 9" cast iron skillet.
To make the filling: In a large mixing bowl, mix the berries, flour and sugar. Transfer the mixture to the prepared pan.
To make the topping: Whisk together the flour and sugar. Work in the butter using a pastry cutter or your hands, mixing until incorporated but a few large chunks still remain.
Sprinkle this mixture over the berries, pinching some of it together into larger pieces.
Bake the crisp for 25 to 45 minutes, until the berries are bubbling and the topping has started to brown (the shorter amount of time for fresh berries, longer for frozen).
Remove the crisp from the oven, and let it cool for several minutes. Serve warm, with ice cream or whipped cream, if desired.