Combine sugar and 1/2 cup water in a 2-quart saucepan set over medium heat. Without stirring, cook mixture until dark amber in color, swirling the pan carefully while cooking, about 20 minutes.
Reduce the heat to low. Slowly add cream, stirring with a wooden spoon. Scrape the vanilla seeds into the pan, and add the pod. Add lemon juice, butter, and bourbon. Stir to combine.
Cover, and store, refrigerated, up to 1 week. Bring sauce to room temperature, or warm over low heat, before using.