COMBINE MILK, first amount of butter, sugar and salt in a small pot and bring to a boil over high heat. Immediately remove from the heat and let stand to room temperature. In the meantime, dissolve the yeast in the water and add it to the milk. Place the liquid in a mixer and add the flour. Using the dough hook, mix until the dough is elastic. It will be sticky. Place in a bowl, cover and let rise until double in bulk, about 1 1/2 hours. Place in refrigerator and chill for 30 minutes. Meanwhile, soften the remaining cold butter by pounding with a rolling pin. Roll the dough on a floured board to form a 1/4-inch thick rectangle. Spread the butter over 2/3 of the rectangle closest to you. Fold the unbuttered third over the center third. Then fold the bottom 1/3 over the doubled portion. Swing the dough around a quarter turn, that is, bring east to south. Roll it again into a 1/4-inch thick oblong. Fold again in thirds. Cover the dough and place in the refrigerator for 2 hours. When the dough is chilled, remove from the refrigerator and repeat the folding and turning twice more. Then roll the dough to 1/4-inch thickness again. Cut the dough into 3-inch squares and cut the squares on the bias to form two triangles. Roll each triangle beginning with the wide side, then shape the rolls into crescents. Chill for 30 minutes in the refrigerator before baking. Preheat oven to 400F. Bake for 10 minutes. Reduce heat to 350F and continue to bake another 15 minutes.