Prepare the vegetables^ Preheat your oven to 190°C/Fan 170°C/Gas 5. Peel and finely chop the onion. Trim and finely chop the carrots (no need to peel unless you want to). Trim the dry ends off the celery sticks, then finely slice them.

Make the lentil sauce^ Place a medium pan on a medium-low heat and add 1 tbsp olive oil. Add the chopped veg, season with salt and pepper and fry, stirring often, for 15 mins till the veg have started to soften and lightly brown. If the veg start to brown too quickly, turn the heat down and add 2-3 tbsp water.

While the veg fry, peel and grate or crush the garlic. When the veg are glossy, add the garlic and 1 tsp fennel seeds and 1 tsp dried oregano and cook, stirring for 1 min.

Tip in the green lentils with the liquid from their tins, then pour in the chopped tomatoes. Add 250ml water. Stir to mix, pop on a lid and bring to a simmer. Simmer for 10 mins, stirring occasionally, till the lentils are tender. The sauce should still be quite soupy. Taste the sauce and add a pinch of salt and pepper if you think it needs it.

Assemble the lasagne^ Spoon1/4 of the lentil sauce into a 21/2 ltr ovenproof dish. Top with 3 sheets of lasagne. Repeat with the lentil sauce and lasagne sheets till you have used them all up, finishing with a layer of lentil sauce. Dot over the ricotta. Slide the dish into the oven and bake for 25-30 mins till browned and bubbling.

Make the garnish^ Whe the lasgane is ready, tka eit out of the oven and let it sit in the dish for 2-3 mins. Put a small frying pan on a medium heat. Pick the sage leaves off the stems. Add 2 tbsp olive oil to the frying pan and toss in the sage leaves. Sizzle for 30 secs till crisp. If you don't want to fry the sage leaves, you don't have to. You can just finely chop them, but frying them makes them extra aromatic and gives them a nice crisp texture.

Spoon the sage leaves and the warm olive oil over the top of the lasagne. Serve it in wedges on warm plates.