Mix butter and flour for beurrage until smooth. Roll into a 10-inch square inside parchment. Chill for 30 minutes.
Combine dry détrempe ingredients. Cut in softened butter. Add water/vinegar mixture and mix until dough forms. Knead gently until smooth. Shape into 6½-inch square. Chill for 30 minutes.
Remove butter 5–7 minutes before dough so both are cold but pliable.
On a floured surface, place dough diagonally on a butter square. Fold butter over dough and seal seams.
Roll to ¼-inch thick (about 18 by 7 inches). Perform one envelope fold. Wrap and chill for 30 minutes.
Repeat two more sets of two single folds (six total turns), chilling 30 minutes between each set.
After the final turn, chill for at least 2 hours or overnight.
Roll to ⅛-inch thick. Chill 30 minutes before cutting.
Bake at 375°F (preferably convection) until deeply golden and fully puffed.
Video
Notes
Technique: Butter must stay cold yet pliable throughout lamination.
Storage: Freeze flat between parchment for up to 2 months. You can refrigerate up to 2 days before using.