Preheat the oven to 190°C/375°F/gas 5. Trim the leeks, then wash and finely slice. Drizzle 2 tablespoons of olive oil into a large frying pan on a medium-high heat and pick in most of the sage leaves. Add the leeks, season with sea salt and black pepper, and fry for a few minutes, or until slightly softened. Pour in the cider, bring to the boil, then cover and cook for 5 minutes, or until tender. Remove from the heat and leave to cool a little.
Roughly tear the bread (crusts and all) into a food processor and whiz to coarse crumbs. Add the breadcrumbs and sausage meat to the cooled leeks, then scrunch and mix together to combine. Grease a 20cm bundt tin or ovenproof dish with olive oil, then fill with the stuffing mixture, level it out and bake for 45 minutes, or until golden and cooked through.
Drizzle 1 tablespoon of olive oil into a medium frying pan over a medium heat, pick in the remaining sage leaves and fry until crisp. Carefully turn out the stuffing crown out onto a plate, scatter over the crispy sage, and serve.