Preheat the oven to 375°F.
In a large bowl, toss together the rosemary, 1/2 cup Parmesan, flour, baking powder, salt, and pepper. Add the butter, and use your fingers to quickly rub together the butter and the flour mixture, until the mixture is full of pea-size lumps. Add 3/4 cup of the buttermilk, and toss together until a sticky dough forms. (Add the remaining 1/4 cup buttermilk by tablespoonfuls if your dough is too dry.)
Turn the dough out onto a well-floured surface and roll or pat the dough into a large 1 1/2-inch-thick circle. Using a 1-inch round biscuit cutter, make 12 biscuits and place on a baking sheet. (You may only get 8 out of the first circle – gather the scraps and roll together to make the additional biscuits.)
Brush the tops of the biscuits with a little milk and sprinkle with the remaining 1/4 cup Parmesan. Bake for 12-15 minutes or until golden brown. Let cool slightly on a cooling rack.
Cut the biscuits in half and spread each with a teaspoon of fig jam and 1/2 slice of prosciutto. Serve immediately.
MAKE AHEAD: These biscuits are best when served the day they are baked. You can save time by either measuring out your ingredients the night before (store them separately, covered, in the refrigerator) or making/shaping them a week in advance and freezing them on a sheet tray until hard (about 1 hour). Transfer to a Ziploc bag and freeze until ready to bake. Simply arrange the frozen biscuits on a baking sheet and bake as normal, adding a few minutes to the baking time.