Dissolve yeast in the warm water. Add next five ingredients plus optional salt, if desired, then beat in the flour. Dough will be sticky. On a floured board, roll out the dough to about 1/8 inch. Cut into 2-inch squares. Heat oil to 370 degrees F. Drop beignets in oil a few at a time. As they puff, turn them to brown other side. Remove, drain, and dust with powdered sugar.