Soak the raisins in the sherry overnight. Place the duck breasts on a plate and cover them loosely with a sheet of greaseproof paper. Leave them in the fridge overnight (this will help dry out the skin and make it extra crispy).
When ready to start cooking, put the sugar and sherry vinegar in a small pan with 1 tablespoon cold water and cook over a low heat until the sugar has completely dissolved. Increase the heat and boil vigorously until the syrup turns into a deep amber-coloured caramel (CAUTION: boiling sugar is extremely hot).
Remove the pan from the heat and add the red wine vinegar (take care as it will bubble quite energetically). Return the pan to the heat, add the soaked raisins and the sherry. Leave to simmer gently for 20 minutes.
Mix the arrowroot with 2 tablespoons water, stir into the sauce and simmer for 1 minute, then add the pine nuts. Season to taste and keep warm over a low heat.
Lightly score the skin of each duck breast in a diamond patter, taking care not to cut down into the flesh. Season the meat with salt and pepper and the skin with just salt.
Heat a dry, heavy-based frying pan over a high heat. Add the duck breasts, skin-side down, lower the heat to medium and cook for 3-4 minutes until the skin is crisp and golden brown. Turn the breasts over and cook them for 5 minutes if you like them pink, or slightly longer if you like them a little more cooked. Remove the breasts from the pan and place on a board. Leave to rest for 5 minutes.
Meanwhile, using the same pan that you cooked the duck in, add a little olive oil and fry the sliced pumpkin for a few minutes.
Heat a little olive oil in a small frying pan and add the shallot. As they start to turn colour, add the girolles and thyme, fry for no more than 1 minute. Season to taste.
Place the pumpkin on warm serving plates. Slice each duck breast diagonally into long thin slices and place alongside the pumpkin. Add some of the girolles around the side of the plate, spoon the sauce over and garnish with the watercress sprigs.