Season the fillets with salt and pepper and put them into a tigh t-fitting shallow pan with the wine and fish stock.
Cover with a lid and bring to the boil.
Then reduce heat and simmer for 2 minutes.
Remove the fillets with a slotted spoon, transfer to a plate and keep warm.
Reduce the remaining liquid by half then stir in the cream.
Simmer until that has reduced by half.
Put the egg yolk into a bowl with 2 tbsp (30 ml) of the sauce and whisk over a pan of simmering water for 1 minute until it becomes light and frothy.
Stir this mixture into the rest of the sauce and add the grapes.
Arrange the sole fillets in an ovenproof dish and spoon the sauce and grapes over the fish.
Place under a hot grill until golden.