Mix yeast and milk together and let sit until yeast has dissolved. Mix in the sugar, salt, and 2/3 cup of the flour. Mix well.
Mix in the rest of the flour, you may need to add more until you get a dry dough that doesn't stick to the bowl. Knead your dough for about 10 minutes then cover with a hot, damp cloth and let it rise for 1 1/2 hours. It's easier clean up to just knead your dough in the bowl then cover it.
Once your dough has risen, wrap it in plastic wrap and place it in the refrigerator for about 30 minutes.
While your dough is in the frig, divide your butter and place each half in between wax or parchment paper, roll out into a rectangular shape and place back in the refrigerator to stay cold.
Remove dough from refrigerator and roll out into a 16x8 rectangle
Place first half of butter in the middle of the dough. Fold one side of the dough over the butter, then place the other half of butter over that and fold the other side of the dough over that half of butter. Roll dough out and repeat this step. Place back in frig for 30 minutes. Repeat this step two more times making sure to place the dough back in the frig after time (fold,roll,frig). After the third time, leave in the frig for two hours or overnight, depends on when you started.
Remove dough from refrigerator and roll dough out into a 16x8 rectangle. Cut the dough down the middle long ways and begin to cut your triangles.
Take each triangle and roll over it once from end to end with rolling pin then roll into crescent shape.
Cover and let rise for a hour. Preheat oven 475' bake croissants for 2 minutes then turn oven down to 375' and continue baking for 11 minutes more.