1.Peel 5 of the zucchini, then coarsely grate all zucchini. In a large frying pan, melt 30g of the butter and add grated zucchini. Cook, stirring, about 10 minutes or until softened and excess liquid is evaporated.
2.Meanwhile, in a medium frying pan, melt remaining butter; cook onions, stirring, until soft. In a medium bowl, combine zucchini, onion and basil.
3.Preheat oven to 200°C (180°C fan-forced). In a medium jug, whisk eggs, creme fraiche or sour cream and ⅓ cup of the grated gruyere cheese.
4.In a 2-litre (8-cup) oiled shallow ovenproof dish, spread zucchini mixture. Top with the egg mixture, swirl with a knife to mix lightly. Sprinkle with ½ cup coarsely grated gruyere cheese. Bake about 25 minutes or until browned lightly.