Position a rack in your oven to the lower-third position (for sea-level, place rack in the center of the oven) and preheat the oven to 365 (F) (for sea-level, preheat the oven to 350 (F)).
Put the oat cookie, brown sugar, and salt in a food processor and pulse it on and off until the cookie is broken down into a wet sand. (If you don't have a food processor, you can fake it till you make it and crumble the oat cookie diligently with your hands.)
Transfer the crumbs to a bowl, add the butter, and knead the butter and ground cookie mixture until moist enough to form into a ball. If it is not moist enough to do so, melt an additional 1 to 1 1/2 tablespoons of butter and knead it in.
Divide the oat crust evenly between 2 (10-inch) pie tins. Using your fingers and the palms of your hands, press the oat cookie crust firmly into each pie tin, making sure the bottom and sides of the tin are evenly covered. Use the pie sheets immediately, or wrap well in plastic and store at room temperature for up to 5 days or in the fridge for up to 2 weeks.
Put both pie shells on a sheet pan. Divide the crack pie filling evenly between the crusts; the filling should fill them three-quarters of the way full. Bake for 20 minutes (for sea-level, bake for 15 minutes) only. The pies should be golden brown on top but will still be very jiggly.
Open the oven door and reduce the oven temperature to 350 (F) (for sea-level, reduce to 325 (F)). Depending on your oven, it may take 5 minutes or longer for the oven to cool to the new temperature. Keep the pies in the oven during this process. When the oven reaches 350 (F) (or 325 (F)), close the door and bake the pies for 5 minutes longer. The pies should still be jiggly in the bull's-eye center but not around the outer edges. If the filling is too jiggly, leave the pies in the oven for an additional 5 minutes or so.
Gently take the pies out of the oven and transfer to a cooling rack to cool to room temperature. Then freeze your pies for at least 3 hours, or overnight, to condense the filling for a dense final product -- freezing is the signature technique and results in a perfectly executed crack pie.
If not serving the pies right away, wrap well in plastic wrap. In the fridge, they will keep fresh for 5 days; in the freezerm they will keep for 1 month. Transfer the pies from the freezer to the fridge to defrost for a minimum of 1 hour before consuming.
Serve crack pies cold with a dusting of confectioner's sugar.