kitchen and chemistry

I'm leaving Sweden in two days, next to my building there is a nice bakery owned by a Spanish woman: Marta. She can make delicious croissantes and kindly she gaves to me the recipe!

Ingredients:
1 kg flour
120 g yeast
30 g salt
200 g sugar
ice cold water
0.75 kg butter

Preparation:
Prepare the dough with all the ingredients except the butter and keep it in the fridge for 1 night (or 3 h in the freezer). Ground it with the rolling pin a square shape and cover the surface with butter. Close the edges on it and ground it in a right-angled shape 7 mm thick. Now you have to fold the sheet in 3x3 (tres veces tres) way: you have to fold the right edge to the center till 2/3 the lenght and so on with the other. At the end you obtain a square one third the size of the former rectangle. You have to repeat this operation three times. The most impotant thing is the temperature: the dough must be cold otherwise the butter will melt and leak out. Is good after the second folding to keep the mass in the freezer for a while. At the end you need a 5 mm thick sheet. Cut in triangle 7 cm base and 12 cm height and make a 2 cm cut in the middle of the base.
Now it comes the difficult part: you have to roll up the slice from the base to the tip. Let them double in size.
Spread on them a beaten egg and bake them at 220 °C for 10 - 20 min (depending on the oven).Good luck!