01 - Dissolve yeast in lukewarm milk. Let stand for 5 minutes until foamy and activated.
02 - Add flour, sugar, salt, and softened butter to yeast mixture. Mix until rough dough forms, then knead for 5–7 minutes until smooth and elastic.
03 - Shape dough into a rectangle, wrap tightly in plastic wrap, and refrigerate for 1 hour to firm.
04 - Place cold butter between parchment paper sheets. Pound and roll into an even 6 x 8-inch rectangle. Refrigerate if soft.
05 - Roll chilled dough on floured surface into a 10 x 14-inch rectangle. Position butter slab on lower half, fold upper half over, and seal edges completely.
06 - Gently roll dough into a 10 x 20-inch rectangle. Fold into thirds like a letter. Wrap and chill for 30 minutes.
07 - Repeat rolling and folding process twice more, rotating dough 90 degrees each time. Chill 30 minutes between each fold.
08 - Roll dough into a 10 x 20-inch rectangle. Cut into 8 equal rectangles. Place chocolate at one end of each and roll tightly into logs, seam-side down.
09 - Arrange on parchment-lined baking sheet. Cover loosely and let rise at warm room temperature for 2 hours until puffy and doubled in size.
10 - Preheat oven to 400°F.
11 - Whisk egg with milk until combined. Brush evenly over proofed croissants.
12 - Bake for 18–20 minutes until deep golden brown with crisp, flaky layers. Cool on baking sheet for 10 minutes before serving.