Preheat the oven to 200 °C.
Score the duck breasts through the skin and fat but not all the way through the meat.
Heat an ovenproof frying pan and fry the breasts, skin side down, until the skin browns and the fat runs out.
Place the duck breasts in the oven and roast for 10 minutes. They should still be slightly pink inside.
Meanwhile, place the verjuice in a saucepan until the pears are tender.
To serve, cut each duck breast into three pieces, place a dollop of pears on a plate, top with the duck and some watercress tossed in extra-virgin olive oil and lime juice.
Pass around a bowl of lime hollandaise sauce.
LIME HOLLANDAISE SAUCE
Put the egg yolks and lime juice in a saucepan over very low heat.
Whisk, adding the butter, piece by piece, until the sauce thickens.
Do not overheat or the eggs will scramble. Season to taste.