Preheat the oven to 450°. In a small bowl, soak the currants in the water and red wine vinegar until plumped, 10 minutes. Drain.
In another small bowl, combine the Champagne vinegar with the 1/2 cup of olive oil (8 tbsp.) and season the dressing with salt and pepper.
On a rimmed baking sheet, toss the bread with 2 tablespoons of the oil. Bake for about 5 minutes, until lightly toasted. Let cool, then tear the bread into bite-size pieces. In a bowl, toss the bread with three-quarters of the dressing and let stand for 30 minutes.
Meanwhile, in a pie plate, warm the pine nuts in the oven for 2 minutes.
In a skillet, heat the remaining 1/2 tablespoon of oil. Add the scallions and garlic and cook over moderate heat until softened, about 2 minutes; transfer to a large bowl. Add the currants, bread, pine nuts and the remaining Champagne vinaigrette and toss.
Spoon the bread salad into a shallow 1-quart baking dish. Cover loosely with foil and bake for about 15 minutes, until heated through. Uncover and bake for a few minutes longer to dry out the top and brown the bottom. Transfer the bread salad to a platter, toss with the arugula and serve.
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