Place pears and pear nectar in a heavy medium saucepan; bring to a simmer. Cover and simmer over medium-low heat, stirring occasionally, until the pears are very tender, 30 to 35 minutes. Cooking time will vary depending on the ripeness of the pears.Advertisement
Mash the pears with a potato masher. Cook, uncovered, over medium-low heat, stirring often, until the puree has cooked down to a thick mass (somewhat thicker than applesauce), 20 to 30 minutes. Stir almost constantly toward the end of cooking. Scrape the pear butter into a bowl or storage container and let cool.
Make Ahead Tip: Store in an airtight container in the refrigerator for up to 2 weeks or freeze for up to 6 months.