Preheat the oven to 200C (400 F/Gas Mark 6).
Soak the prunes over-night (or for as long as possible) in the Madeira. The next day, heat the oil and butter in a medium pan and sweat the onion for 2-3 minutes until softened. Add the breadcrumbs, stirring to bring them together. Transfer to a bowl and add the pork belly, apple, lemon zest, parsley and sage. Season well and stir to combine.
Shape a little of the stuffing into a round the size of a golf ball and then flatten slightly. Sit a prune on top and reshape the stuffing back into a ball to enclose the prune in the centre. Wrap a piece of streaky bacon around the ball securely and place in a roasting tray.
Repeat to make about 12 stuffing balls. Drizzle the stuffing balls with 2 tablespoons of the goose fat (taken from the roasting goose above) and roast for 10-15 minutes until the bacon is crisp and the stuffing just catching colour.
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