Heat half the butter butter in a medium saucepan and add onion. Cover and cook on a medium low heat, stirring occasionally for 5-10 minutes or until onion is soft.

Meanwhile place stock in another pan and bring to a simmer.

When the onion is soft, add the unwashed lentils and increase the heat to medium high. Stir for a minute.

Add 2 ladles of stock. Stir well then simmer for 3-4 minutes or until the stock is absorbed.

Repeat until the lentils are tender and oozy. If you run out of stock, use water.

Add remaining butter and cheese and stir until combined. Taste and season. Serve with extra parmesan shaved over.