In a bowl, combine the water, yeast, and sugar. Let stand for 5 minutes.
In another bowl, combine the flour and salt. Add the yeast mixture and stir with a fork until a soft dough forms. Add a little flour if necessary.
Knead for 1 minute in the bowl while adding flour to prevent sticking.
Cover with a clean cloth. Let the dough rise for about 30 minutes in a warm place, away from drafts (in the microwave oven, for example).
On a floured surface, roll out the dough into two 20 cm (8 in) diameter discs.
In a cast iron skillet, heat half the butter and cook one bread over medium heat for about 3 minutes on each side. Repeat with the remaining butter and bread. Cut into wedges and serve hot.