To prepare dressing, place cardamom in a spice or coffee grinder; process until finely ground. Combine the cardamom, buttermilk, and next 5 ingredients (buttermilk through pepper).
To prepare salad, arrange 3 endive leaves on each of 4 salad plates. Top each with 3/4 cup orange sections, 1/4 cup radish, 1/4 cup onion, 2 tablespoons dates, and 1 teaspoon mint. Drizzle each serving with 1 tablespoon dressing.