Meanwhile, preheat the oven to 350ºF (180ºC). Place 6 heart shapes on each cookie sheet, about 3 inches apart. Top each one with a piece of chocolate bar. I placed my chocolate pieces on the upper left of each cookie. Bake the cookies until the tops look set, about 10-11 minutes. Be careful not to over bake the cookies or they’ll be more difficult to shape into hearts.