Combine the ice water and buttermilk in a small pitcher and chill until needed. In the bowl of a food processor, combine the sweet rice, oat, and millet flours with the cornstarch, tapioca flour, ground chia seed, sugar, and salt. Scatter the butter pieces over the top and place the lid on the food processor, but don’t process yet! Simultaneously pour the cold buttermilk mixture through the feed tube in a slow and steady stream while pulsing the food processor all the while until all the liquid is added and the butter is broken down into chunks of varying sizes from tiny peas to lima beans. The dough should hold together when squeezed; if it needs more liquid to come together, gently pulse in a tablespoon or two more ice water.

Press the dough into a ball, flatten into a disc in a large piece of plastic wrap, wrap tightly, and chill for up to 3 days.

Let the dough soften at room temperature for 10 – 20 minutes to make it easier to roll. On a surface dusted lightly with oat flour, roll the chilled dough out into a rough square that is about ¼" thick. As you work, dust the top of the dough with oat flour, using a dry pastry brush to sweep away the excess. If the dough begins to stick to the work surface, use a bench scraper to move it to one side, dust the surface with more flour, and return the dough to the surface to continue rolling. Don’t worry if the dough crumbles and wants to fall apart, just press it back together. Once the dough is rolled out, fold it in thirds like folding a letter, then roll it up from a skinny end into a loose spiral. Gently press to flatten it slightly, and chill for 30 minutes. Optionally (preferably), repeat this step once more. The dough will get smoother and easier to work with as you make these turns.

Divide the dough into two portions of approximately two-thirds and one third. Roll the larger piece of dough into a 12-inch round, dusting with flour as needed to prevent sticking, and ease the dough into a 9-inch pie plate. Trim the dough to a ¾-inch overhang and fold it under itself. Crimp the crust with your thumbs and forefingers, and prick the bottom all over with the tines of a fork. Chill until firm, at least 30 minutes, or wrap and chill for up to 1 day.

On a surface dusted lightly with oat flour, roll out the smaller piece of dough to a 9-inch (23-cround about 1⁄4-inch (6-mthick. Use a fluted cookie cutter or biscuit cutter (or small glasto cut out shapes measuring about 2-inches in diameter. Place the dough shapes on a small baking sheet lined with parchment paper and chill until firm, 20 minutes. Optionally, press the dough scraps together, wrap and chill until firm, and repeat the rolling/cutting process once more.

Position a rack in the lower third of the oven, top with a baking stone if you’ve got one and preheat to 425ºF (220ºC). Line a rimmed baking sheet with parchment paper for easy cleanup.

To make the filling, in a large bowl whisk together the sugar, cornstarch, cinnamon, cayenne, and salt to combine. Add the cherries and bourbon, tossing to combine, and let sit 10-20 minutes to draw out the juices a bit.

Spoon the fruit and juices into the chilled crust, smoothing it flat. Place the chilled dough shapes over the top of the fruit, overlapping them slightly and leaving lots of windows for the steam to escape. Brush the rounds with the cream or milk and sprinkle with the smoked or coarse sugar.

Place the pie on the lined baking sheet and slide into the oven on the baking stone. Bake at 425ºF (220ºC) for 15 minutes, then decrease the oven temperature to 375ºF (190ºC) and continue baking until the crust is golden and the fruit is bubbling thickly, 35–50 more minutes. (Err on the side of overbaking lest you wind up with soupy filling that doesn't set.) Let the pie cool completely to set the fruit, at least 2 hours, then cut into wedges and serve at room temperature with ice cream. The pie is best shortly after baking and will keep at room temperature for up to 1 day, or refrigerated for up to 3 days.