Preheat the oven to 180 C. Peel and chop up the butternut squash. Place it on a lined baking tray, drizzle with olive oil and sprinkle over rosemary. Season with salt and pepper. Bake for 20 minutes and keep it aside.
Heat 2 tsp of olive oil in a skillet, over medium heat. Add garlic and sauté for 30 seconds. Add in diced onions and sauté till caramelised. Add in chopped kale and cook till wilted.
Roll out the pastry to about 5mm thickness and place it over a tart pan. Gently press the pastry into the pan and trim out any excess from the edges. Use a fork to prick the bottom of the dough. Blind bake for 20 minutes.
Meanwhile prepare the custard. In a bowl, whisk together two eggs, crème fraiche, milk and nutmeg. Season with salt and pepper.
Remove the pastry from the oven. Add in the roasted butternut, kale and caramelised onions. Pour in the custard and add crumbled feta. Bake for 40-45 minutes until golden. Let it cool for 10 minutes before serving.