Transfer the pine nuts to a small bowl. Put the shallots, garlic, vinegars and reserved orange juice into the saute' pan. Bring to a bowl over low heat. Stir in the black pepper (to taste), then pour the dressing over the spinach and watercress. Toss to coat. Arrange mixture on salad plates, spoon orange segments atop each and garnish with the pine nuts and, if you like, orange wheels. MAKING ORANGE WHEELS Slice an unpeeled orange into 1 cm rounds. Make a cute halfway across each round, from the peel to the core, and twist the sides of the cut in opposite directions so that the top half of the round will stand upright when placed on the salad.