For the flatbread: In a medium bowl, combine the yeast, sugar, and warm milk and let the yeast bloom. Mix in the rest of the ingredients and add the water; combine and knead thoroughly until you have a smooth dough. Set aside for 1 hour in a warm place. Divide the dough into six portions, and shape them in to tennis size balls. Brush a little olive oil on top of each dough ball and cover with a piece of cloth for at least 30 minutes. Flatten each ball of dough like a pancake by tossing and slapping with both hands; roll out to about 1/8 inch. Brush with olive oil and grill on both sides until cooked, about 4 minutes per side.

To finish the flatbreads: In a small bowl, combine the crème fraiche, lemon zest and juice, olive oil, and herbs. Stir to combine. Top each warm flatbread with a dollop of the herbed crème fraiche, a few slices of the prosciutto, and a handful of grapes. Garnish with a few mint leaves over the top, drizzle with olive oil, sprinkle with salt if desired, and serve.