Step 1 In a small mixing bowl (preferably plastic or ceramic), sprinkle the yeast over the water. Set the bowl aside for a few minutes to give the water time to absorb the yeast. Using a wooden spoon, stir in the bread flour until all of the ingredients are thoroughly combined.
Step 2 Cover the bowl tightly with a sheet of plastic wrap, then tightly wrap another piece of plastic wrap or twine around the perimeter of the bowl to further seal the bowl.
Step 3Set the bowl aside at room temperature (ideally 68 to 70 degrees) until the sponge becomes bubbly and thick, like the consistency of wallpaper paste (thicker than a pancake batter but thinner than dough), 12 to 24 hours.