Soften the raisins in warm water for ten minutes, then drain and squeeze out the water. Wash the spinach several times and dry it well using a salad spinner. Put the leaves in a large bowl and sprinkle with the raisins, grated pecorino and lightly toasted pine nuts (to toast them, warm a small non-stick frying pan and toss the pine nuts in it for a few minutes without using any seasoning). Season with salt, add the vinegar, olive oil and some freshly milled pepper. Mix delicately so as not to damage the leaves.