Dice pears into medium sized pieces. Remove the seeds and stem if not using a food mill. Peel pears, if desired.
Combine the diced pears, water, lemon juice, vanilla extract and cinnamon, nutmeg, and star anise, if using, in a large saucepan.
Cover with a lid and bring to a boil over medium high heat.
Reduce heat to medium-low and simmer, stirring occasionally, until pears are soft, about 25-30 minutes or until the pears are mush when pressed with a fork. Remove star anise, if using.
Use an immersion blender to process the sauce until smooth. Add the brown sugar.
Reduce the heat to medium and simmer for 30-45 minutes, stirring occasionally, scrapping the caramelized pear butter from the bottom.
Once the pear sauce has cooled completely, portion into glass or plastic containers. Cover and store in the refrigerator. The pear sauce will keep in the fridge for one week. You can also freeze or can the pear sauce.
The longer the sauce reduces, thickens and caramelizes, the more prone to burning it becomes. To avoid scorching the sauce, reduce the heat as it cooks or continually stir the sauce.
The longer the sauce cooks, the darker, sweeter and thicker the sauce will become.