If using instant yeast, add flour, salt, sugar and yeast to a large mixing bowl and whisk to combine (*If using active-dry yeast, see Note below). Add the lukewarm water to the bowl and mix until the dry ingredients are absorbed. The dough will be very sticky.
Cover the bowl with a towel (or plastic wrap) and place in a warm area to rise about 1 hour.
After it has risen to twice its size, preheat oven to 425 degrees and grease two 1 or 1.5 quart oven-safe bowls with 1 Tb. of butter in each bowl.
Using two salad forks, punch down the dough and scrape the dough down from all sides of the bowl. Using the forks, separate the dough into two even portions (it may be tricky since it's very soft and sticky). Carefully lift one half out of the bowl into the first buttered bowl, then transfer the other to the second buttered bowl. Try to just scoop it up quickly and dump into the bowls (yes, it will be messy).
Let dough rise another 20-30 minutes, in a warm place, covered with a towel or plastic wrap. The dough should rise to just above the lip of the bowl, or just below it, if it's a little deeper (like a 1.5 quart bowl).
Place bowls directly onto the rack of pre-heated oven and bake for 15 minutes.
Reduce heat to 375 degress and bake another 15-17 minutes.
Remove from oven and turn onto a cooling rack (the loaves should pop out easily).
Cool for about 10 minutes before cutting/serving.