To make caramel, melt butter over low heat in heavy saucepan. Add cream, sugar and caramels. Stir continuously until caramels are melted, remove from heat and stir in vanilla. Let caramel cool a few minutes, stirring it occasionally, until it thickens slightly. (If caramel separates it will come together with stirring and cooling.) Spoon the warm caramel over the rows of pecans on each log.