Stir together the flour, salt, and sugar with a spoon. Add the eggs and the sponge until the ingredients form a coarse ball. If there is any loose flour, dribble in a small amount of water or milk to gather it into the dough. Mix for about 1 minute, then let rest for 10 minutes. Divide the butter in 4 pieces and work into dough, one piece at a time while mixing. After mixing about 4 minutes, the dough will change from sticky to tacky and eventually come off the sides of the bowl. If not, sprinkle in more flour to make it do so.