01 - Dissolve yeast in warm milk with 1 teaspoon of sugar in a small bowl. Let sit for 5 minutes until mixture becomes foamy.
02 - Combine flour, remaining sugar, and salt in a large bowl. Add melted butter, egg, and activated yeast mixture. Stir until combined, then knead for 5-8 minutes until smooth. Shape into a ball, cover, and refrigerate for 1 hour.
03 - Place cold butter between two sheets of parchment paper. Pound and roll into a 6x6 inch square. Refrigerate until firm.
04 - On a floured surface, roll chilled dough into a 12x12 inch square. Position butter block at center and fold dough edges over butter, sealing completely.
05 - Roll dough into a 16x8 inch rectangle. Fold into thirds like a letter. Rotate 90 degrees, roll out, and fold again. Wrap and refrigerate for 30 minutes.
06 - Repeat rolling and folding process one more time, then refrigerate for an additional 30 minutes.
07 - Roll dough into a 16x10 inch rectangle. Cut into 8 triangles. Starting from wide end, roll each triangle toward tip. Place on parchment-lined tray, cover, and let rise in warm place until puffy, about 1-2 hours.
08 - Preheat air fryer to 320°F. Brush croissants with egg wash. Place 2-4 croissants in basket without overcrowding. Air fry for 8-10 minutes until golden brown and cooked through. Repeat with remaining croissants.
09 - Cool slightly before serving warm.