Finely dice the onion, garlic, carrots and celery and soften gently in olive oil until the veg is tender and fragrant.
Add the lentils, toast briefly and pour in the chopped tomatoes and passata. Stir in the Italian herbs and simmer gently until the lentils are soft. Season to taste with salt and pepper.
For the béchamel, melt the butter, stir in the flour and cook briefly. Gradually whisk in the milk until the sauce is smooth and creamy, then season with salt, pepper and nutmeg.
Spread a little lentil bolognese over the base of a baking dish, then layer lasagne sheets, lentil bolognese and béchamel alternately. Finish with sauce on top so the sheets stay moist.
Scatter over the Emmental and bake the lasagne at 180 °C (160 °C fan) for 30–40 min until the top is golden brown and the edges are bubbling slightly.
Leave to rest briefly before cutting, then serve hot. A green salad with olive oil goes very well with it.
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This lasagne is down-to-earth and really comforting. It's full of flavour, juicy and refreshingly uncomplicated. Just the thing when you want the oven to smell like home.