To bake in an oven, preheat to 400° F. To bake over campfire, make sure you have a nice hot fire with lots of coals at the ready! A lid for the pan is recommended, as well, although foil to cover the pan will certainly do.
Prepare an cast iron skillet (or 8×8 or 9×13 baking dish for oven method) by oiling the bottom and sides lightly (a smaller pan will yield a thicker crisp and will need to bake longer).
In a large bowl, stir to combine all filling ingredients. Set aside while preparing the topping.
Combine all dry topping ingredients in a large bowl, then cut in the butter using a pastry cutter, two butter knives, your fingers, or an electric mixer or large food processor. The mixture should be like clumpy gravel in texture when the butter is incorporated. Don't over-work the mixture or the butter will start to get melty.
Pour the fruit filling mixture onto the bottom of the prepared pan and sprinkle with the topping until covered evenly.
Bake in the oven for approximately 30 minutes, or until the fruit is bubbling and the topping is lightly browned.
To cook over a campfire, place a well-fitted cast iron lid on top of the pan (or cover with foil, crimped at the edges with a couple of holes poked to vent steam) and place on a rack over the open campfire. If using a lid, cover top of lid with hot coals and cook for approximately 20-30 minutes, checking often. If using foil, place over the campfire for 45-60 minutes until nicely browned.
Serve warm as it is, or top with ice cream or non-dairy “ice creams”.