For the rösti, place the grated potato onto a clean tea towel and squeeze over a bowl to remove the excess liquid. Place the grated potato into a clean bowl.
Add the herbs to the bowl, season with salt and freshly ground black pepper and mix well.
Heat the butter with the oil in a frying pan over a medium heat. Place the potato mixture into the pan, pressing down to make a round cake. Fry the rösti for 4-5 minutes on each side, using a fish slice to carefully turn it over, until crisp and golden-brown.
For the sole Véronique, season the flour with salt and freshly ground black pepper and dust the fish with the flour to lightly coat it, shaking off any excess.
Heat the butter in a frying pan over a medium heat and fry the fish for 1-2 minutes on each side.
Add the white wine and simmer until reduced by half.
Add the cream and simmer until the sauce is slightly thickened and the fish is cooked through.
Remove from the heat, add the lemon juice and grapes and stir well.
To serve, place the rösti onto a plate, top with the fish and pour over the sauce.