Mix ground beef, onion, salt, pepper and mint together and set aside. Mix yogurt and garlic and let come to room temperature. Slice the stack of won ton wrappers in half and then half again until you have 4 stacks of small square wrappers. Place a small amount of meat mixture in the center of each square. Dampen the edge of the wrappers and bring all four corners up and seal together. Place them on a baking sheet. Preheat oven to 375 degrees. Bake for 15 minutes or until lightly browned. Remove from the oven and place in a large baking dish and pour heated chicken broth over. Bake for 15 minutes. Remove from oven and transfer to serving bowls. Pour yogurt-garlic mixture over the top. Whisk together the butter, paprika and cayenne and pour over yogurt sauce. Sprinkle with mint leaves and serve.