01 - Dissolve yeast in lukewarm milk. Let sit for 5 minutes until foamy.
02 - Add flour, sugar, salt, and softened butter to yeast mixture. Mix until a rough dough forms. Knead for 5–7 minutes until smooth.
03 - Shape dough into a rectangle, wrap in plastic, and refrigerate for 1 hour.
04 - Place cold butter between two sheets of parchment. Pound and roll into a 6 x 8-inch rectangle. Chill if soft.
05 - Roll dough on a floured surface into a 10 x 14-inch rectangle. Place butter slab on one half, fold over the other half, sealing edges.
06 - Roll dough gently into a 10 x 20-inch rectangle. Fold in thirds like a letter. Wrap and chill for 30 minutes.
07 - Repeat rolling and folding (turning 90 degrees each time) two more times, chilling 30 minutes between folds.
08 - Roll dough into a 10 x 20-inch rectangle. Cut into 8 rectangles. Place chocolate at one end of each rectangle. Roll tightly into a log, seam-side down. Place on a parchment-lined baking sheet.
09 - Cover loosely and let rise at warm room temperature for 2 hours, until puffy.
10 - Preheat oven to 400°F.
11 - Beat egg with milk. Brush croissants with egg wash.
12 - Bake 18–20 minutes until deep golden and crisp. Cool slightly before serving.