In a heavy saucepan, combine 1½ cups of the sugar and the cream over moderately high heat. Stir the mixture until the sugar begins to melt. Place the thermometer in the mixture and cook until it registers 220° or the soft ball stage.

Meanwhile, place the remaining ½ cup sugar in a heavy saucepan and stir constantly over moderate high heat until the sugar melts and begins to turn a golden caramel color.

Pour the hot cream mixture into the caramelized sugar and stir in the pecans. With a large soup or dessert spoon, immediately spoon out the mixture onto a cool marble surface or onto a sheet of parchment paper. Allow to cool.