01 - Whisk together gluten-free flour, almond flour, sugar, yeast, and salt in a large bowl until thoroughly combined.
02 - Combine warm milk, warm water, egg, and softened butter in a separate bowl. Pour the wet mixture into the dry ingredients and mix until a sticky dough forms.
03 - Shape the dough into a rectangle, wrap tightly in plastic wrap, and refrigerate for 45 minutes to relax the gluten-free structure.
04 - Slice cold butter into thin slabs. Place between parchment paper sheets and pound or roll into an even 6 x 8-inch rectangle. Chill briefly if butter becomes too soft.
05 - Roll chilled dough on a lightly floured surface into a 12 x 8-inch rectangle. Position butter layer over the bottom two-thirds of dough, leaving a border. Fold top third down over butter, then fold bottom third up (letter fold).
06 - Rotate dough 90 degrees, roll to 12 x 8-inch rectangle, and fold as before. Repeat rolling and folding process twice more, chilling for 20 minutes between each turn to maintain cold temperature.
07 - After completing the fourth fold, wrap dough and refrigerate for 1 hour before shaping.
08 - Roll dough into a 16 x 10-inch rectangle. Cut into 8 equal triangles using a sharp knife or pizza cutter. Roll each triangle tightly from the wide end to the point, then place point-side down on a parchment-lined baking tray.
09 - Cover croissants loosely and let rise in a warm, draft-free area for 1 to 1 1/2 hours until slightly puffy and expanded.
10 - Preheat oven to 400°F (200°C) while croissants finish proofing.
11 - Whisk egg and milk together. Brush croissants lightly but thoroughly with egg wash for a golden, glossy finish.
12 - Bake for 20 to 22 minutes until deep golden brown and cooked through. Cool slightly on the baking tray before serving warm.