Preheat the oven to 200C/400F/Gas 6.
For the salmon, rub the salmon with the oil and season well with salt and freshly ground black pepper.
Place into a hot frying pan and fry for 3-4 minutes on each side, or until cooked through.
For the vegetables, place the vegetables onto a baking tray, drizzle with the oil and season well with salt and freshly ground black pepper. Transfer to the oven and roast for 15-20 minutes, or until golden-brown and cooked through.
For the French fries, heat the oil in a deep heavy-bottomed pan, until a breadcrumb sizzles and turns brown when dropped into it. (CAUTION: hot oil can be dangerous. Do not leave unattended.)
Place the potato sticks into the oil and deep-fry for 5-6 minutes, until crisp and golden. Carefully remove with a slotted spoon and drain on kitchen paper.
For the sauce, melt the butter in a pan and fry the spring onions until softened.
Add the cream and milk and heat to a gentle simmer.
Add the cooked potato and season, to taste, with salt and freshly ground black pepper. Transfer to a food processor. Allow to cool for a few minutes, then blend until smooth.
To serve, pour the sauce onto a warmed plate and place the salmon on top. Place the roasted vegetables around the edge of the plate and serve the French fries in a bowl alongside.