Mix both the flours, the salt, the rosemary, the instant baking powder, and oil, then knead. Add the water while continuing to work the dough for about 5 minutes, then roll out the dough until obtaining a thickness of about 8 mm, and cut out more little flatbreads as possible. Put the flatbreads into a greased pan, prick their surfaces with a fork, and cook them for about 5 minutes. Turn the flatbreads and cook again for 5 minutes, until they are golden and crisp. Put the sliced red onions and the sugar in a pan with very little water and oil and let them caramelize, stirring occasionally. Place the caramelized onions and a slice of Prosciutto Toscano DOP on each flatbread and serve.