Knead all ingredients together, except the Croissant Butter, for around 8 minutes.
Place the dough into a container and let it rest at ambient temperature, for 1 hour. Store in the refrigerator.
Next day: laminate the dough and fold in the Millefeuille Butter. Tour the butter for 2 x 4 folds and 1 x 3 folds. Let the laminated dough set over night
Stretch the croissant dough at 7 mm and shape the croissants. Let them proof before baking.
