Heat a little olive oil and gently fry the onion and apple for about 5 minutes, until softened. Add the sage for the last 30 seconds. Leave to cool slightly.
Combine the cooled mixture with the pork mince, sausage meat, parsley, breadcrumbs, salt and white pepper. Fry a small piece to check the seasoning before shaping, then form 3 to 4 patties.
Fry the burgers over a medium heat until cooked through. For larger patties, brown them in the pan then finish in a 180°C / 350°F oven for about 15 minutes.
For the slaw, combine the cabbage, fennel, apple and coriander. Mix the mayonnaise with the chipotle and lemon juice, season, and dress the slaw just before serving.
Butter the buns and grill them cut side down until golden.
Build the burgers with mayonnaise, a patty and a generous pile of slaw.