01 - Whisk together gluten-free flour, almond flour, sugar, yeast, and salt in a large mixing 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, cohesive dough forms.
03 - Shape the dough into a rectangular block, wrap tightly in plastic wrap, and refrigerate for 45 minutes to firm up.
04 - Cut cold butter into thin slabs. Place between parchment paper sheets and pound or roll into an even 6 x 8-inch rectangle. Return to refrigerator if softening occurs.
05 - Roll chilled dough on a lightly floured surface into a 12 x 8-inch rectangle. Position butter layer over 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 again. Repeat rolling and folding process twice more, chilling for 20 minutes between each turn.
07 - After completing the fourth and final fold, wrap dough and refrigerate for 1 hour to rest completely.
08 - Roll chilled dough into a 16 x 10-inch rectangle. Using a sharp knife or pizza cutter, cut dough into 8 triangles. Roll each triangle tightly from the wide end toward the point.
09 - Place shaped croissants on a parchment-lined baking sheet, point side down. Cover and let rise in a warm, draft-free area for 1 to 1.5 hours until slightly puffy.
10 - Preheat oven to 400°F.
11 - Whisk egg and milk together until blended. Brush the surface of each proofed croissant lightly with the egg wash mixture.
12 - Bake croissants for 20 to 22 minutes until deep golden brown and flaky. Allow to cool slightly on the baking sheet before serving.