Preheat the oven to 375℉ and rub a little butter into a 9×9-inch baking dish.
Prepare the filling: In a large bowl, gently stir together the cherries, granulated sugar, tapioca flour, and lemon juice. Pour the filling into the prepared baking dish in an even layer, adding any juices in the bowl.
Prepare the topping: In a medium bowl, stir together the oats, oat flour, almond flour, brown sugar, baking powder, cinnamon, and salt. Pour in the melted butter, then stir until the mixture is completely moistened.
Sprinkle the topping evenly over the cherries, and place in the oven to bake for 50-60 minutes, until the filling is bubbly and the topping is golden. If the topping seems like it's browning too much for your liking, gently place a piece of foil over it to protect it. Remove from the oven and let stand for at least 10 minutes before serving.
Notes
Tips
Use the topping with other fruit! Yes, this topping is the best crisp topping I make and you can handily perch on top of other crisp fillings. Try it atop blackberries, plums, apples, peaches, and so much more.
Oat flour substitute - Use sorghum or teff flour, or try a gluten-free all-purpose flour blend.
Almond flour substitute - You can use another nut flour of choice for the almond flour, substitute oat flour, or make a gluten free flour blend swap for the combination of oat and almond flour.
Tapioca flour substitute - I prefer tapioca flour/starch to thicken filling recipes, but cornstarch is a fine substitute. Use 2 tablespoons of cornstarch if you make the swap. Or, use 4 tablespoons of arrowroot powder for the tapioca flour.
Make it dairy-free - Use cold coconut oil in place of the butter if you wish to make this crisp without dairy.
Make it refined sugar-free - Substitute coconut sugar for the brown sugar in the topping, and try coconut sugar or honey in the filling for the granulated sugar.
Add nuts - Sliced almonds added to the topping are lovely and add a little crunch, turning the crisp topping very granola-like.
Storage
Counter - Cover the baking pan with foil and keep it on the counter for up to 2 days.
Fridge - Place leftover crisp in an airtight container or cover the pan tightly with foil and store it in the fridge for up to 5 days.
Freezer - If you wish, you can freeze the baked crisp in a freezer-safe pan, tightly wrapped in foil, for up to 3 months. Defrost the crisp in the fridge before reheating.
To Reheat - Place the cherry back in the oven at 250°F either in its original baking pan or transfer it to an oven-safe dish to gently rewarm it until the filling is heated through and the topping is slightly crisp.