Preheat the oven to 200C/400F/Gas 6.
For the tomato sauce, heat the oil in a heavy-based ovenproof pan. Add the onion and garlic and fry gently for a few minutes until softened, but not coloured.
Add the tomatoes and balsamic vinegar, then season, to taste, with salt and freshly ground black pepper.
Stir well, then transfer to the oven for 6-8 minutes, until the sauce is slightly reduced and thickened.
For the pancakes, sift the flour into a bowl with a pinch of salt.
Make a well in the centre and break in the eggs. Gradually whisk together, adding the milk a little at a time to make a smooth batter.
Grate the courgettes and stir into the batter.
Heat the oil in a frying pan and add spoonfuls of the courgette batter. Cook for 2-3 minutes, or until tiny bubbles begin to form on the surface and the underside of the pancakes are lightly golden. Turn over and cook for another 1-2 minutes, until cooked through and lightly golden.
To serve, place the courgette pancakes onto warmed plates and spoon over the tomato sauce.