This elegant fish dish adds a touch of bistro sophistication to the week with golden and crisp fillets resting atop a beautiful, buttery mash mixed with seasonal greens. Drizzled with a satiny lemon butter pan sauce, there'll be many compliments to the chef (that's you!).
Peel and cut potatoes into 3cm pieces. Place in a saucepan of cold, salted water, cover and bring to the boil. Cook for 15 minutes or until tender. Drain well. Return to saucepan with half the cream and half the butter, and mash until smooth. Season with salt and pepper.
Remove leaves from cavolo nero stalks, discarding stalks. Finely slice cavolo nero leaves. Cut green top from leek and discard. Halve leek lengthwise, rinse under cold water and finely slice. Pick dill fronds from their stems and roughly chop.
Heat 20ml (1 tablespoon) oil in a medium frypan over medium heat. Add leek and a pinch of salt and cook, stirring, for 5 minutes or until softened. Add cavolo nero and cook, stirring occasionally, for a further 5 minutes or until completely wilted. Combine this mixture with the mashed potato along with most of the dill and season with salt and pepper to taste. Set aside and keep warm.
Heat remaining oil in a frypan over medium heat. Season fish with salt and pepper. Add fish, skin-side down, and cook for 5 minutes or until crisp. Turn and cook for a further 2-3 minutes, or until just cooked through. Remove from pan and rest for a few minutes while you make the sauce.
To make the sauce, juice the lemon. Add lemon juice, remaining butter, Dijon mustard and remaining cream to the pan and place over medium heat. Bring to a rapid simmer and cook sauce for 2 minutes or until slightly reduced. Season with salt and pepper.
Divide potato mash between plates and top with fish. Drizzle with the lemon pan sauce and scatter with remaining dill to serve.