Preheat the oven to 180C
Put the olive oil in a large, lidded frying pan. Add the courgettes and herbs and season with salt and pepper.
Cover and cook gently for 10 minutes, stirring every so often, until the courgettes have softened slightly but are still al dente. The oil should have taken on a deep, rich green colour from the courgettes.
Transfer to a GN container. Whisk the crème fraîche, milk and flour together in a bowl and season with salt. Pour this mixture over the courgettes – it will not be enough to completely cover the courgettes, but this is fine – it will bubble up when cooking.
Sprinkle over the cheese. Bake in the oven for around 15 minutes, or until brown and bubbling.