Step 1

Fry the onion in the olive oil over a medium-low heat for 5-6 mins or until tender, then stir in the garlic and fry for further minute until fragrant. Add the courgettes, turn up the heat slightly, and fry for 5-6 mins or until the water that comes off them evaporates and the mixture begins to soften – the courgettes should look fairly dry and reduced in size. Remove from the heat.

Step 2

Heat the oven to 200C/180C fan/gas Beat together the ricotta, mascarpone, lemon zest, basil, half of parmesan, the nutmeg, salt and lots of black pepper in a bowl. Stir three-quarters of the mixture into the courgettes and combine well.

Step 3

Add a spoonful of the filling into the base of a roughly 22cm x 35cm lasagne dish and smooth over to cover the base. Add a layer of parma ham, then a layer of lasagne sheets, trimming to fit if you need to. Repeat the layers (about four) until all the fillings have been used up, finishing with a pasta layer.

Step 4

Beat the egg yolk into the reserved ricotta mixture and spoon over the top, smoothing to the sides in an even layer. Scatter with the remaining parmesan. Bake for 35-40 mins or until the top is golden and bubbling, and a knife inserted into the middle meets little resistance. Serve with a sharply dressed green salad and some salted wedges of beef tomato, scattered with more basil.