Before you start, preheat oven to 220°C (or 200°C fan bake). Bring a medium pot of salted water to the boil.
Prep potatoes and cook in pot of boiling water for 15-20 minutes, until very tender. Drain and leave to steam for 5 minutes, then return to pot. Mash well with sour cream, truffle oil and salt. Season to taste with salt and pepper. Keep warm.
Cut beetroot in half and prep thyme. Toss beetroot, carrots, thyme, leeks and oil on a lined oven tray. Season with salt and pepper and roast for about 25 minutes, until tender and golden.
Trim duck breasts of overhanging fat and score skin at 1cm intervals. Pat dry and season with salt. Heat oil in a medium fry-pan on medium-high heat. Cook duck, skin side down, for about 5 minutes to render fat.
Flip duck and sear a further 1 minute, until lightly browned. Remove vegetables from oven and transfer duck to tray (reserving pan). Return tray to oven for 5 minutes, or until duck is medium. Rest, covered, before slicing thinly. Return vegetables to oven for any remaining cook time.
Prep shallot and mushrooms. Wipe reserved pan clean and return to medium heat with oil. Add bacon and cook for about 2 minutes, until golden. Add shallot and mushrooms and cook for about 4 minutes, until mushrooms are tender. Remove pan from heat, add jus and a splash of water. Stir through butter.
Serve mash and vegetables topped with duck and sauce.