Preheat the oven to 200°C/400°F/gas mark.
Place the duck breasts in a large bowl and use your hands to rub in the olive oil with some salt and pepper.
Place the oiled breasts on a hot griddle, skin-side down first, and seal for about 2 minutes on each side. Transfer to a roasting tin and roast in the oven for about 8 minutes until crisp on the outside but pink in the middle. Remove from oven and leave to rest for 1 minute before slicing each breast on the diagonal into six.
For the sauce::
Melt half the butter in a large frying pan, add the peppercorns and cook over a medium heat for 1 minute. Add the limoncello with the lemon zest and juice and simmer until reduced by half.
Add the chicken stock, season with salt and pepper and continue to cook for about 8 minutes until the sauce is reduced by half again. Add the remaining butter to the sauce and stir with a wooden spoon until you create a creamy texture.
Place the sliced duck in the pan with the sauce and continue to cook for 1 minute allowing the flavour of the limoncello to coat the meat. Sprinkle with fresh mint and serve immediately.
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