Preheat the oven to 200 degrees fan setting.
Heat a generous glug of olive oil in a heavy based oven proof casserole pan over a gentle flame and cook the leeks gently for about 10 minutes or until softened.
Add the cavolo nero and savoy cabbage, handfuls at a time if necessary and allow the greens to wilt down.
In a separate bowl, combine the breadcrumbs with the hazelnuts and lemon zest with enough olive oil to lubricate the mixture.
Toss a good pinch of salt through the greens then pour over the cream and grate in the nutmeg.
Bring the cream to a gentle simmer then switch off the heat and stir through the grated Grana Padano and lots of cracked black pepper.
Transfer the greens to the oven proof dish or if cooking in an oven proof pan already simply sprinkle over the topping.
Grate over more Grana Padano and cook for 20 minutes until bubbling and golden.
