Prep the pears: Peel, core, and coarsely chop the pears.
Cook until very soft: Combine pears, maple syrup, and bourbon in a 6-quart stainless steel or enameled Dutch oven. Bring to a boil, then reduce heat and simmer uncovered for about 20 to 30 minutes, stirring often, until the pears are very soft. Remove from heat and cool slightly.
Puree the mixture: Puree the pear mixture in batches in a food processor until smooth, transferring each batch to a bowl. Return all puree to the Dutch oven.
Cook down until thick: Bring the puree to a boil, then reduce heat and simmer uncovered until it thickens, darkens, and holds its shape on a spoon . Stir occasionally at first, then stir more often as it thickens to prevent scorching.(see notes)
Fill jars: Ladle hot pear butter into a hot half-pint jar, leaving 1/4-inch headspace. Remove air bubbles, adjust headspace if needed, and wipe the rim clean. Center the lid on the jar and apply the band, adjusting to fingertip-tight. Repeat with remaining jars.
Process in a water bath canner: Place jars in a boiling water canner, ensuring they are fully submerged. Process 10 minutes, adjusting for altitude.
Cool and check seals: Turn off heat, remove the canner lid, and let jars stand 5 minutes. Remove jars and cool undisturbed for 12 to 24 hours. Check seals, label, and store.