Make the Dough (Détrempe):
In a large bowl, combine flour, sugar, salt, and yeast. Add water and milk, stirring to form a shaggy dough. Mix in butter pieces until just incorporated. Knead briefly, shape into a rectangle, wrap, and refrigerate overnight.

Prepare the Butter Block:
Form butter into a 6×6-inch square between parchment sheets. Chill until firm but pliable.

Laminate the Dough:
Roll the dough into a 12×12-inch square. Place butter in the center (diamond orientation), fold corners over to enclose. Roll into a long rectangle and complete 3 single folds (letter-style), chilling between each fold.

Shape the Croissants:
Roll laminated dough into a large rectangle. Cut into triangles and roll tightly from base to tip. Curve ends inward slightly.

Proof the Croissants:
Place on lined baking sheet and let rise at room temperature 1.5–2 hours until doubled in size and puffy.

Bake:
Preheat oven to 375°F (190°C). Mix egg yolk and cream, brush over croissants. Bake 18–22 minutes or until deeply golden and crisp. Let cool slightly before serving.