Warm the oil in a medium pan over a medium heat, add the onion, season and saute gently for five minutes. Remove the sausage from its skin and crumble into the pan with the garlic, breaking up the sausagemeat with a spoon so it doesn’t clump together.
Once the onion is soft and the pork has coloured a little, add the lentils, fennel seeds, chilli and sage, and stir to coat in the fat. Add the tomatoes and milk, and simmer for 20 minutes.
Heat the oven to 180C (160C fan)/350F/gas 4. Bring a deep pan of salted water to a boil. Cut out and remove the backbones of the cabbage leaves and cut the leaves into two or three pieces.
Blanch the leaves in the boiling water for a few minutes to soften; do this in a few batches. Once they’re cooked, transfer to a colander to drain.
Stir the eggs and 75g parmesan into the ricotta and season. Spoon a third of the sausage ragu into a large baking dish and cover with a third of the cabbage leaves
. Repeat twice more, then spoon on the ricotta mix and spread it over the top. Sprinkle with the remaining parmesan and drizzle with a little oil, cover with foil and bake for 15 minutes.
Remove the foil and return to the oven for another 15-20 minutes, until the top is beautifully risen and golden.