Peel and chop pears into 1/4-inch pieces; discard seeds. Place pears and next 5 ingredients (through lemon) in a large bowl; toss to coat. Let stand at room temperature 6 hours (or refrigerate overnight), stirring occasionally.
Pour pear mixture (including accumulated juices) into a large heavy saucepan or enameled cast-iron pot. Cover with water to 1/2 inch above fruit. Bring to a simmer over medium heat. Reduce heat to medium-low; cook 1 1/2 to 2 hours or until fruit achieves a jammy consistency, stirring frequently toward the end of cooking. Remove from heat; stir in vinegar. Cool. Store in refrigerator up to 2 weeks.
Recipe adapted from Slow Fires. Copyright 2015 by Justin Smillie. Published by Clarkson Potter/Publishers, an imprint of Penguin Random House LLC. $40, 320 pages.