Mix the dry ingredients: In the bowl of a stand mixer, combine 160 g (1 cup) brown rice flour, 115 g (1 cup) tapioca starch, 75 g (1/2 cup) potato starch, 50 g (0.25 cup) granulated sugar, 8 g (1.5 teaspoons) kosher salt, 7 g (2.25 teaspoons) instant yeast, 6 g (2 teaspoons) xanthan gum, and 8 g (2 teaspoons) baking powder. Whisk to combine evenly.
Make the psyllium gel: In a small bowl, whisk together 16 g (2 tablespoons) whole psyllium husk and 160 g (2/3 cup) warm water until thickened into a gel. Set aside for about one minute to hydrate fully.
Combine the wet ingredients: In a medium bowl, whisk together 160 g (2/3 cup) warm whole milk, 1 (1 egg) large egg, 42 g (3 tablespoons) unsalted butter, and 5 g (1 teaspoon) apple cider vinegar. Add in the psyllium gel and whisk until smooth and uniform.
Make the dough: Pour the wet ingredients into the dry ingredients. Using the dough hook attachment, mix on medium speed for about 5 minutes, scraping the sides and bottom of the bowl as needed. The dough should be soft, thick, and slightly sticky.
First roll: Lightly dust your work surface with tapioca starch. Turn out the dough and pat into a rough rectangle. Roll into a 10×14-inch rectangle about ¼-inch thick.
Add the frozen butter: Using a box grater, grate 42 g (3 tablespoons) unsalted butter(frozen) evenly over the entire surface of the dough, leaving no bare spots.
First letter fold: Fold the right third of the dough over the center, then fold the left third over that. Give the dough a quarter turn so the whole thing is now horizontal in front of you.
Second roll and fold: Roll the dough back out into a 10×14-inch rectangle. Fold the right third over the center, then fold the left third over that. The dough should feel cool but pliable.
Roll into cylinder: With your hands, roll up the folded dough from the short side into a cylinder (it will look like a massive cinnamon roll) to distribute the butter layers evenly, then roll out with the rolling pin into a 14-inch circle about ⅛-inch thick.
Cut the crescents: Using a pizza cutter or sharp knife, cut the circle into 12 equal wedges (like cutting a pizza).
Shape the rolls: Starting from the wide end of each wedge, roll toward the point. Place seam-side down on a parchment-lined baking sheet, leaving about 2 inches between each roll. Curve the ends slightly inward to create the classic crescent shape.
Proof the rolls: Cover loosely and let rise in a warm spot (75–80°F) for about 45–60 minutes, or until puffy and nearly doubled in size.
Bake: Preheat the oven to 375°F (190°C). Brush the tops with 1 (50 grams) egg (beaten) for shine. Bake for 18-22 minutes, or until golden brown and the centers reach 200°F.
Finish: While still warm, brush the tops with 14 g (1 tablespoon) melted butter and sprinkle lightly with ½ teaspoon flaky sea salt. Let cool for a few minutes before serving.