Trim off the leaves and the root end of the celery. Slice the stalks diagonally into thin semicircles, cutting across the entire head, then put aside.
Core the apples but do not peel. Slice finely and put aside.
Generously cover the bottom of a large frying pan with olive oil, and heat until it shows a haze. Snip the sage leaves into the pan. Peel the garlic and crush it in. Allow the sage and garlic to sizzle for a few seconds, then quickly add the celery, apples and bay leaf and stir well.
After 1 minute, pour in enough white wine to cover the mixture. Continue cooking over high heat for 2–3 minutes, stirring occasionally, until the celery is cooked but still crunchy. If the mixture dries out before the celery is cooked, add a little more wine.
When the celery is done to your liking, stir in the capers, if using, and heat through quickly. Season the dish with salt and black pepper to taste, discard the bay leaf and serve immediately.