In a dry heavy saucepan, cook sugar over moderately low heat, stirring slowly with a fork until melted and pale golden.

Continue to cook the caramel, without stirring, swirling the pan occasionally, until it reaches a deep golden color.

Remove the pan from the heat and carefully add the heavy cream, bourbon, lemon juice, and toasted chopped pecans (be cautious as the caramel will steam and harden).

Return the pan to the heat and simmer the sauce, stirring continuously, until the caramel is completely dissolved, approximately 5 minutes.

Pour the finished sauce into a bowl and allow it to cool slightly.

Store the sauce, covered and chilled, for up to 2 weeks.