For the flour blend
168 grams superfine white rice flour (60%)
62 grams potato starch (22%) (See Recipe Notes)
34 grams tapioca starch/flour (12%)
16 grams potato flour (6%) (See Recipe Notes)
1 teaspoon konjac powder (also called glucomannan powder)
For the biscuits
Flour blend from above
1 tablespoon baking powder
1/4 teaspoon baking soda
1/2 teaspoon kosher salt
8 tablespoons (112 g) unsalted butter, cut into a 1/4-inch dice or grated and kept very cold
1 cup (8 fluid ounces) buttermilk, chilled
2 tablespoons (28 g) unsalted butter, melted
About potato flour
Please use potato flour if at all possible. If not possible, you can replace the 16 grams of potato flour with the same amount (by weight) of additional superfine rice flour.
If you can’t use potato flour because you can’t have potatoes, try replacing the potato starch with cornstarch or arrowroot.
Preheat your oven to 425°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.
Set a large mixing bowl over a digital kitchen scale. Measuring by weight and hitting “tare” on your digital scale to zero out the weight of the bowl, add the superfine white rice flour, potato starch, tapioca starch, and potato flour, zeroing out each ingredient after it’s added. Add the konjac powder by volume, and whisk to combine well.
To the same bowl, add the baking powder, baking soda, and salt, and whisk to combine well. Add the diced or grated and chilled butter, and mix to combine, flattening any large clumps in the butter with the back of your mixing spoon. Add the buttermilk and mix until combined.
Working quickly, so the dough doesn’t get warm, drop the batter by the quarter cup using two large spoons or a 2-inch ice cream scoop about 1 1/2-inches apart on the prepared baking sheet. Using a pastry brush or the tips of your fingers, brush the all exposed sides of the mounds of dough generously with the melted butter.
Place the baking sheet in the center of the preheated oven and bake until lightly golden brown all over (about 15 minutes). Remove from the oven and allow to set briefly before serving.