First, make your pesto. Put your herb of choice into a small blender along with the roughly chopped garlic, pine nuts, 25g of the grated cheese (reserve 25g to sprinkle on top of the lasagne), lemon juice, and extra virgin olive oil. Blitz until you have a paste. You might need to add a little more oil to get the right consistency. Season to taste, and put the pesto to one side. You can also use a jar of ready-made pesto; you will need 150g.
Thinly slice the courgettes, either by hand or with a mandolin (carefully), and fry in the oil over a medium heat for 5-6 minutes until softened and taking on a little colour. Add the grated garlic, 1/2 tsp sea salt and a good grinding of black pepper, and cook for another 2 minutes.
In a separate saucepan, add 200g mascarpone, 250ml vegetable or chicken stock, and 150g of your pesto - either homemade or from a jar. Heat gently, stirring until smooth, then add the fresh or dried oregano and set aside.
In a baking dish (roughly 18 x 25cm), put ⅓ of your creamy pesto sauce, a ⅓ of the sliced courgettes, and finally ⅓ of the walnuts. Layer on 4 of the fresh lasagne sheets. Repeat these layers twice, ending with a layer of lasagne.
Stir the milk into the remaining 50g of mascarpone in the tub. Pour this white sauce all over the lasagne, ensuring it’s well covered. Sprinkle on the Parmesan/Pecorino cheese. Place in the middle of the oven (not at the top as it will brown too quickly) and bake for 30-35 minutes until golden on top and bubbling well.
This dish goes well with a crisp green salad and perhaps some garlic bread.