The night in advance: dissolve yeast into the water, into the mixer's bowl sift 2/3 of the two flours, pour the yeast/water mixture and mix for a couple of minutes.Add one egg, mix, when it has been absorbed add the second egg, mix again.Add now the sugar and the flour ( but save 2 spoons ), mix for about 10 minutes.
Add salt, mix two minutes, add the soft butter and the spoons of flour: now let the mix knead the dough for about 15 minutes, it must be very smooth and elastic.Put the dough into a greased bowl, cover with cling film and store in the fridge overnight ( or for about 8 hours).
In the morning: take the butter for layers out of the fridge, let it get as soft as the dough ( so not fridge hard but not creamy, pay attention to this).
Roll the dough square shaped, put in the centre the butter forming a square with it too then, pinching the edge of the corner, fold the dough to the centre of the square over the butter. Do it with all the dough corners.Roll again the dough into a long rectangle, fold the up shorter side to the half of the rectangle then fold over the lower side ver the folded one. Cover with cling film, let it rest in fridge for 30 minutes then roll again the pastry keeping the " spine" on your left and repeat the rectangle folding.Let it rest in fridge for 30 more minutes then repeat folding.
Now roll the dough about 0.3 inches tall and cut triangles out of the rectangle.If it's too big, cut the dough in two with a sharp knife.Try not to discard any piece of pastry as this dough cannot be re-kneaded.If the ends aren't perfect triangles it's not important: they may not be beautiful but they surely are as good as the other croissants!
Now make a small cut at the base of the triangles and roll them to form the croissants.
Now you have two solutions: put the croissants on a baking tray, cover them with cling film, let them rise, brush with some beaten egg and bake at 430°F for 5-6 minutes then finish the baking lowering temperature to 30°F OR put the croissants on a baking tray, cover with cling film and put into the freezer.When they will be hard you can put them into a plastic bag.When you want them for breakfast just remove croissants from the freezer the evening before and bake them straight in the morning.