Combine ricotta, half the pecorino, the buttermilk, nutmeg and grated rind in a large bowl.

Heat oil in a large frying pan over medium-high heat, add garlic, half the green onion and 400g (12½ ounces) of the mushrooms; cook, covered, for 5 minutes or until mushrooms start to soften. Add 300g (9½ ounces) of the cavolo nero; stir until wilted. Cool slightly.

Preheat oven to 180°C/350°F.

Grease a 3-litre (12 cup) ovenproof dish. Spread base with ¼ cup of the ricotta mixture. Top with a single layer of lasagne sheets, trimming to fit. Top with one-third of the remaining ricotta mixture and half the mushroom mixture. Continue layering, ending with ricotta mixture.

Cover lasagne with foil. Bake for 25 minutes. Remove foil; bake a further 20 minutes or until pasta is cooked through and top is golden brown.

Meanwhile, heat extra oil in a medium frying pan over high heat; cook remaining mushrooms and remaining cavolo nero, stirring, for 3 minutes. Add remaining green onion, the hazelnuts, rind strips and chilli; toss to combine.

Serve lasagne topped with mushroom mixture and remaining pecorino.