Preheat the oven to 180C/365F/Gas 4.
For the crispy potato rösti, cook the potatoes in boiling water for 7 minutes. Drain and set aside to cool slightly.
Peel the potatoes and grate into a bowl. Stir in the onions and garlic and season, to taste, with salt and freshly ground black pepper.
Set four 10cm/4in chefs' rings on a baking sheet and divide the potato mixture between them, pressing down to form cakes. Chill in the fridge for 20 minutes.
Heat the oil in a frying pan. Remove the potato cakes from the chef's rings and fry for 4-5 minutes on each side, or until golden-brown on both sides.
Remove from the pan and set aside to drain on kitchen paper.
Meanwhile, for the sole Véronique, season the fillets, to taste, with salt and freshly ground black pepper. Carefully roll the fillets up, with the skin-side facing inwards, and place into an ovenproof dish.
Pour over the stock, cover with aluminium foil and bake in the oven for 15-20 minutes, or until the fish is cooked through.
Remove the fish from the oven and carefully pour the cooking juices into a frying pan along with the vermouth. Heat the mixture until boiling and cook until the volume of the liquid had reduced by two-thirds.
Stir in the cream and lemon juice and cook until the volume of the liquid had reduced by a half. Stir in the grapes.
To serve, place a potato rösti onto each of 4 serving plates, top with 2 sole fillets and spoon over the sauce.
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