Preheat the oven to 200C/180C Fan/Gas 6.

Butter an ovenproof dish approximately 25 x 16 x 6 cm (use a larger, shallower tray if you prefer)

Put the lentils in a sieve and rinse under a cold tap.

Tip the lentils into a medium saucepan and add the stock or water. Bring to the boil then turn down the heat and simmer very gently until all the liquid has been absorbed (20-30 min).

Take off the heat and set aside.

While the lentils are cooking: take a medium frying pan and add the oil and butter.

Over a low-medium heat cook the onions, seasoned with a little salt & pepper, until softening and a little brown (10-15 min).

Add the mushrooms, garlic, dried sage plus a little more salt & pepper, and continue cooking until the mushrooms are browned too (8-10 min). Take off the heat.

Add the contents of the frying pan to the cooked lentils. Stir in the yeast extract if using along with the grated cheese and parsley.

Stir in the beaten eggs then pour the mixture into the prepared baking dish.

Put in the oven and bake until risen and cooked all the way through. A skewer or cocktail stick should come out clean. (Approx 35 min, less if you used a baking dish with a larger base).

Cut into 4 and serve with green vegetables or salad and baked potatoes if liked.

Leftovers can be kept in the fridge for 2-3 days or frozen once cold.

Reheat in a microwave or low-medium oven covered in foil.