Place the bread in a dish and pour over half the measurement water, then leave to soak for 20 minutes.
Put the almonds and garlic in a food processor and pulse until very finely chopped. Add the bread with its soaking liquid and the oil and blend until smooth. Season with salt and pepper, then gradually blend in the remaining measurement water until the consistency of single cream.
Chill for at least 2 hours, then ladle into bowls, scatter with the grapes and serve drizzled with a little extra olive oil.