Combine pears, cider and bourbon in a large Dutch oven and bring to a boil over medium-high heat. Reduce heat to medium-low, cover and simmer, stirring occasionally, until pears are very soft, about 20-25 minutes.
Using a slotted spoon, transfer pears to a food mill and process until dry skins are all that remain. Scrap the bottom of the food mill as a lot of the puree will stick. Discard skins and transfer puree back into the Dutch oven. Stir in sugars, lemon juice and salt. Simmer over low heat (otherwise, it will splatter!), stirring occasionally, until mixture is browned and thickened and rubber spatula or wooden spoon leaves distinct trail when dragged across bottom of pot, about 45 minutes to 1 hour. Transfer pear butter to a jar with tight-fitting lid and let cool to room temperature before refrigerating. Pear butter can be refrigerated for up to 1 month.
I didn't get the pear variety from the farmer I purchased them from, but they looked like Bartletts.
If you can't find 1816, use your favorite bourbon, preferably one with similar characteristics (check out the tasting notes here).
This recipe is adapted from the Apple Butter recipe in America's Test Kitchen D.I.Y Cookbook.