From a tree — your own, a neighbour's, a friend's. Rarely sold. Pick young, unblemished, bright green ones.
Worth knowing
Infuse torn leaves in hot cream or milk for ice cream and panna cotta, then strain; or wrap fish or goat's cheese in a leaf to grill so the scent steams in. Toasting them briefly first makes it deeper and nuttier. The sap can irritate skin, so rinse your hands.