In a large pan heat up the oil, add the bay leaf, garlic and onion and fry for 3 minutes until softened. Add the lentils, kale, tomatoes and passata, seasoning and spices, most of the water, stir and cover. Simmer for about 35 minutes or until the sauce has thickened and the red lentils are fully cooked, stirring often. Remove from the heat, stir in the parmesan and add the rest of the water. Adjust the seasoning if needed.
Preheat the oven to 375 F/ 190 C/ gas mark 5. Grease the bottom of a rectangular lasagne dish (approx. 20 cm x 30 cm) with 1 tablespoon of oil. Set aside.
To make the white sauce in a saucepan melt the butter over a medium heat, add the corn flour and whisk quickly until smooth. Pour in the milk, increase the heat and whisk until the sauce thickens and starts bubbling up. Remove from the heat, season lightly and set aside.
Assemble the lasagne. Cover the bottom of the lasagne dish with 3 lasagne sheets. Pour in half of the lentil sauce and smooth out. Place 3 more lasagne sheets over the top pressing in gently and cover with the rest of the sauce. Cover with the 3 remaining sheets, press gently, pour over the white sauce and sprinkle the cheddar over the top.
Bake in the middle of the oven for 1 hour. Half way through cover the lasagne loosely to prevent it browning too much.
Remove from the oven, set aside for 5 minutes and serve.
Lentils: I used a combination of red and Puy lentils. If you can't find Puy lentils you can use ordinary green lentils.
Spices: I only used oregano and paprika but you can also use basil or thyme if you like. Use a combination of these spices or just one of them. Entirely up to you.
Cheese: I used a moderate amount but you can adjust the amount according to your preference.
Bechamel sauce: The sauce should be quite thick and cover the top lasagna sheets evenly.
Lentil sauce: Taste the sauce before assembling the lasagne to ensure it is well seasoned.
Best served immediately. Leftovers can be refrigerated for up to 3 days. Reheat in a microwave.