The Dough (10 hours ahead)
Dissolve the sugar and salt in one-third of the water. In a separate bowl, mix the yeast into the remaining water, then add the powdered milk.
Place the flour in a mixer bowl. Then, on low speed, using the dough hook, beat in first the sugar mixture, then the yeast mixture. Stop beating as soon as all ingredients are well mixed and the dough comes away from the bowl (approx. 7minutes). DO NOT overwork the dough.
Rising: Cover the dough with a tea towel and leave to rise in a warm place (75 degrees with NO drafts) for about 30 minutes.
Knock back the dough by quickly flipping it over with your fingers to release the carbon gases. DO NOT overwork the dough now or it will be too heavy. Cover with plastic wrap and place in the refrigerator for 6 to 8 hours.
Cut an X in the top of the dough. On a lightly floured surface, roll the ball of dough in 4 places, from the center out, so you roll out a shape that looks like a head with four ears. Put the butter in the center. The butter should be cold but not solid. Fold the four ears into the center.
Lightly flour the work surface and roll the dough into a rectangle about the size of a medium cookie sheet. Then fold that into 3 sections on top of each other. Cover with plastic wrap and chill. Repeat this process 3 times.
Roll the dough again to the size of a medium cookie sheet. Cut the dough into two long strips. Cut squares and cut the squares in half to form triangles. You should have 16 to 18.
Place the triangles on a surface and roll them toward you so the pointy end stays underneath. Put them on a baking sheet and turn the ends in to form the crescent shape.
Lightly brush the croissants with eggwash, working from the inside outward so that the layers of dough do not stick together. Leave to rise in a very warm, preferably humid area free of draft (75 to 85 degrees) until they have doubled in size (approx. 2 hours).
(You can now freeze the croissants for later baking or continue with the recipe. If croissants were frozen, you thaw them before baking.)
To Bake: Lightly glaze them again with eggwash. Put in an oven preheated to 450 degrees and bake for approx. 15 minutes.