Melt the chocolate in the top of a double boiler over simmering water. Add the butter and whisk in the condensed milk, cinnamon, and vanilla. Stir until thoroughly combined. Refrigerate the mixture until firm enough to shape into small balls (about walnut-size), about 2 hours. Roll in crushed pecans, if desired.
Can be stored, covered with plastic wrap, in the refrigerator 2 to 3 days.