How to Make It
In a bowl, cover the raisins with the warm water and let stand until plumped, about 10 minutes. Drain.
In a small skillet, toast the pine nuts over moderate heat until fragrant and golden brown, about 4 minutes. Let cool.
In a medium saucepan, combine the vinegar, sugar, red onion and fennel seeds. Simmer over moderate heat until thickened, about 25 minutes. Pour into a heatproof bowl and let cool to room temperature.
Stir the raisins, pine nuts, grapes and olive oil into the syrup. Season lightly with salt and serve.