For the butter croissants, remove the puff pastry from the package and roll out.
Cut the puff pastry into 3×5 cm rectangles and the butter into thin slices. Place 2 pieces of butter slices on each piece of puff pastry and roll up the puff pastry diagonally.
Brush with yolk and bake the butter croissant in the oven at 180 °C top/bottom heat for about 15 minutes until light.