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