Before you start, preheat oven to 220°C (or 200°C fan bake).
Prep shallot and cabbage. Heat oil in a medium pot on medium heat. Add shallots and cook about 2 minutes, until starting to soften. Add remaining cabbage ingredients and reduce to low heat. Cover with a paper cartouche (see tip below) and cook for 25-30 minutes, until cabbage is soft and liquid has reduced. Stir occasionally. Keep warm.
Prep butternut. Toss on a lined oven tray with oil and French seasoning. Roast on upper oven rack for about 20 minutes, until tender.
Trim duck breasts of overhanging fat. Score skin at 1cm intervals. Pat duck dry and season with salt and pepper. Heat a medium, dry fry-pan on medium-high heat. Cook duck, skin side down, for about 5 minutes to render fat. Flip and sear a further 1 minute, until lightly browned.
Transfer duck to tray with pumpkin and bake for 5 minutes, or until medium. Rest, covered and return butternut to oven for remaining cook time. Reserve 1 Tbsp of duck fat from pan. Wipe pan clean and reserve.
Prep leeks. Place on a second lined oven tray, season with salt and carefully pour over reserved duck fat. Cook on lower oven rack for 7-8 minutes, until lightly browned and tender.
To finish, return reserved pan to low heat, add jus and bring to a simmer for 1 minute, until warm. Thinly slice duck and whisk any resting juices into jus.
Serve pumpkin, cabbage and leeks topped with duck and jus.