In a large bowl, whisk together the flour, salt, sugar, and instant yeast. Add the water. Using a rubber spatula, mix until the water is absorbed and the ingredients for a sticky dough ball.
Cover the bowl with a damp tea towel or plastic wrap and set aside in a warm spot to rise for 1 to 1½ hours, until the dough has doubled in bulk.
Set a rack in the middle of the oven and preheat it to 425 degrees. Grease two 1-quart oven-safe bowls with the softened butter—be generous. Using two forks, deflate the dough by releasing it from the sides of the bowl and pulling it toward the center. Rotate the bowl quarter turns as you deflate, turning the mass into a rough ball.
Using your two forks and working from the center out, separate the dough into two equal pieces. Use the forks to lift each half of the dough into a prepared bowl. If the dough is too wet to transfer with forks, lightly grease your hands with butter or oil, then transfer each half to a bowl. Do not cover the bowls. Let the dough rise on the countertop near the oven (or another warm, draft-free spot) for 10 to 20 minutes, until the top of the dough just crowns the rims of the bowls.
Transfer the bowls to the oven and bake for 15 minutes. Reduce the heat to 375 degrees and bake for 17 to 20 minutes more, until evenly golden all around. Remove the bowls from the oven and turn the loaves out onto cooling racks. If the loaves look pale, return them to their bowls and bake for 5 minutes longer. Let the loaves cool for 15 minutes before cutting.