Preheat the oven to 425F. Thinly slice the zucchini. Cook them in a steamer for 5 minutes. Drain well and pat with kitchen paper to dry completely. Place the zucchini in a 9 x 12-inch gratin dish and season with salt and pepper. Sprinkle with the feta cheese. In a food processor or blender, combine the garlic and basil and pulse until finely chopped. Stir in the eggs and cream. Pour the cream mixture over the zucchini-cheese mixture. Bake for 15 minutes at 425F, then reduce the heat to 350F and cook for 30 minutes longer, until golden on top.
