For the homemade cottage cheese, place the milk into a heavy-based pan and heat until the milk reaches 37C/99F (check using a digital thermometer). Remove the warmed milk from the heat and stir in the rennet.
Set the pan aside to rest, until the milk begins to set. Cover and chill in the fridge for one hour, or until the mixture has set into a soft cheese.
Moisten a length of cheesecloth and use it to line a sieve placed over a large bowl. Using a slotted spoon, transfer the cheese mixture into the cheesecloth-lined sieve and leave in the fridge for 30 minutes, or until most of the liquid has drained away. Discard the liquid and set the cottage cheese aside.
For the ravioli, melt the butter in a frying pan and cook the spinach for 2-3 minutes, or until wilted. Transfer to a colander and set over a bowl to drain. Lightly squeeze the spinach to remove any excess liquid, then roughly chop.
Mix the chopped spinach together with the strained cottage cheese and season, to taste, with salt, freshly ground black pepper and the nutmeg.
Lay a wonton wrapper and flat on a clean work surface. Place a teaspoon of the spinach and cottage cheese mixture into the centre of the wrapper, then brush the edges of the wrapper with the beaten egg. Fold the wrapper over and seal around the edges, making sure there are no air pockets in the ravioli. Using a pastry cutter, cut around the edges of the ravioli to create a semi-circle shape.
Repeat with the remaining wonton wrappers and spinach and cottage cheese filling.
For the courgettes and sage butter, preheat the grill to high.
Melt the butter in a frying pan over a medium-low heat until foaming, then add the sage leaves and leave to gently cook for 3-4 minutes (make sure the sage does not burn), until aromatic. Remove from the heat.
Lay half of the courgette slices on a baking tray, then place the sage leaves used to make the sage butter on top and cover with the remaining courgette slices. Spoon over a little bit of the sage butter and place under the grill for 5-6 minutes, or until the courgettes are tender.
For the ravioli, bring a large pan of salted water to the boil and add the ravioli. Cook for 2-3 minutes, or until the ravioli are al dente. Remove with a slotted spoon.
To serve, divide the grilled courgette slices equally among four serving plates and arrange 4-5 ravioli per person on each plate. Spoon over some of the remaining sage butter and garnish with the sage leaves.
