Gently heat whole plums in a heavy saucepan and simmer over low heat until they collapse. Place in a tamis (a drum-shaped strainer popular in Indian cooking) or over a fine-mesh strainer and push through as much as possible, discarding stems, pits and skins. Return purée to saucepan and, over low heat, stir in honey and lemon juice until combined. Remove from heat and stir in vanilla, salt and peppercorns. Cool to room temperature.
Spread purée about ¼-inch thick on dehydrator tray, Silpat or parchment-lined baking sheet, making sure to leave a 1-inch border free. Dry in dehydrator (145 degrees) or low-temperature oven until leather feels fairly dry to the touch and peels easily from the sheet, up to 20 hours.
To store, cut into strips, sandwich between pieces of plastic wrap or parchment paper and roll up. Tie rolls with butcher’s twine, if you like, and seal in an airtight container.
Makes 2 sheets