Peel and chop the Apple (1/2 cup).
Preheat your oven to 350 degrees F (180 degrees C) and grease your doughnut pan.
Combine the Almond Meal (3 tablespoon), Oat Flour (1/2 cup), Sweet Glutinous Rice Flour (1/2 cup), Pure Cane Sugar (3/4 cup), Baking Powder (1 teaspoon), Ground Cinnamon (1 teaspoon) and Salt (1/2 teaspoon) in a large bowl, mixing well.
In another bowl, whisk the Egg (2) together. Then add Buttermilk (1/4 cup), Unsweetened Apple Sauce (1/4 cup), and Vanilla Extract (1 1/2 teaspoon).
Pour the wet mixture into the dry ingredients and stir with a large wooden spoon until just combined, being careful not to overmix.
Gently fold the diced apple into the batter.
Spoon the batter into the doughnut molds filling to just below the top of each mold, 1/8 in - 1/4 in from the top. Bake for 18-22 minutes until lightly golden brown around the edges. A toothpick inserted in the center should come out clean.
Let cool in the pan for 5 minutes. Slide a thin spatula around the edges of the doughnuts to help loosen them out.
Place on a cooling rack and allow to fully cool before topping.
Preheat your oven to broil over low heat and place a rack at the top position. Place an oven-safe wire rack on a rimmed baking sheet.
Mix the Pure Cane Sugar (3/4 cup) and Ground Cinnamon (3/4 teaspoon) in a bowl. Melt the Butter (4 tablespoon) in a separate bowl.
Brush the doughnuts on all sides with the butter.
Coat fully with the cinnamon sugar mixture on each side.
Place each doughnut on a wire rack and then place under the broiler, watching closely for 1 to 3 minutes until the sugar starts to bubble and melt.
Remove from the oven and gently flip over (the doughnuts will be soft and fragile while hot). Broil again for another 1 to 3 minutes, and then remove from the oven.
As the doughnuts cool they will firm and form a crunchy outer coating. Serve warm.