1. Heat a skillet to medium and cook prosciutto until crispy on both side, about 3-4 minutes per side. Remove from skillet and add walnuts, brown sugar, cayenne, and whiskey (or water). Cook, stirring, until sugar has dissolved and coated walnuts, about 5 minutes. Remove from heat and set aside.
2. In a small bowl whisk together olive oil and white wine vinegar. Season with salt and pepper. Set vinaigrette aside.
3. Combine persimmon, watercress, goat's cheese, and walnuts on a plate. Drizzle with vinaigrette and top with prosciutto slices.