Tip the raisins into a heatproof bowl and pour over enough boiling water to cover. Leave to soak for 10 minutes or until plumped up.
Heat 2 tablespoons of the oil in a large frying pan, add the spinach and stir around the pan until just starting to wilt. Remove from the pan and, when cool enough to handle, squeeze away any excess water.
Wipe the pan clean, then add the remaining oil and cook the pine nuts for 1 minute until starting to colour. Add the garlic and cook for a further 1 minute until it starts to change colour.
Pour in the sherry, drain and add the raisins and cook until almost evaporated, then return the spinach to the pan and heat through. Season to taste with salt and pepper and serve.