Score the skin of each duck breast with a very sharp knife first: you can pop the knife in the freezer for a few minutes to make it easier. Score the fatty skin of the duck breast in a criss-cross manner, but be careful not to cut all the way through the meat.
Season the duck with salt and freshly ground black pepper to taste. Pour the oil into a thick, flat-based pan and heat to a high temperature. Place the breasts into the pan, skin-side down. Cook at a fairly high temperature for about a minute, until the skin renders, taking care not to burn the fat.
Once the skin is golden-brown and crisp, turn the breasts over with tongs and sear the other side for about a minute. Return it once again to the pan, skin-side down, and cook for about 5-8 minutes until cooked all the way through.
Meanwhile, mix the honey and Chinese five-spice powder together in a small bowl.
When the duck is cooked, remove from the pan, brush with the honey and spice and allow to rest in a warm place for at least 5-8 minutes.
For the sauce, heat a lidded frying pan on medium heat and add 25g/1oz of the butter, the shallots and a pinch of salt.
Cook the shallots without the lid until softened, but not coloured - about 2-3 minutes.
Add the wild mushrooms and lemon juice and cover with a lid. Cook for a further minute.
Add the water, bring to the boil and whisk in the remaining butter.
Season with salt and freshly ground black pepper and then add the tarragon.
Heat the oil in a separate frying pan and add the spinach. Cook until the spinach has wilted.
To serve, divide the spinach between four plates, slice the duck breasts in half lengthways and place on top of the spinach, and spoon the mushroom sauce around.
