1. Prepare your jars and water bath. Place 5 to 6 half-pint jars in a large pot of water and bring to a simmer. Keep jars hot until ready to fill. Place 2 small plates in the freezer for gel testing. Set lids in a small bowl of hot water.

2. Peel and crush the peaches. Score a shallow X on the bottom of each peach, blanch in boiling water for 30 seconds, then transfer to an ice bath. Slip off the skins. Remove pits and crush the peach flesh with a potato masher until you have about 4 cups of chunky crushed fruit.

3. Combine fruit and sugar. Add the crushed peaches, lemon juice, grated apple, and sugar to a wide, heavy-bottomed pot. Stir over medium heat until the sugar fully dissolves, about 3 to 4 minutes. The mixture will smell sweet and floral.

4. Cook at a full rolling boil. Add the butter, raise heat to high, and bring the mixture to a full rolling boil that cannot be stirred down. Stir frequently to prevent scorching. The jam will begin to deepen from pale orange to a warm amber-gold.

5. Test for gel stage. After 10 minutes of boiling, drop a small spoonful onto a frozen plate. Wait 60 seconds and push the jam with your fingertip. If it wrinkles and holds its shape, it is set. If it runs, continue cooking for 2 to 3 more minutes and test again. The jam should read 220 degrees F on a candy thermometer.

6. Add flavor add-ins. Remove the pot from heat. Stir in cinnamon, bourbon, or vanilla seeds if using. Skim any remaining foam from the surface with a flat spoon.

7. Fill the jars. Ladle the hot jam into hot sterilized half-pint jars, leaving 1/4 inch of headspace. Wipe the jar rims clean with a damp cloth. Apply lids fingertip-tight.

8. Process in a water bath. Lower jars into the boiling water bath, ensuring they are covered by at least 1 inch of water. Process for 10 minutes. Remove and let cool undisturbed on a towel for 12 hours. Listen for the lids to pop as they seal.