Before you start: you will need a large, deep, ovenproof frying pan. Preheat your oven to 220°C (200°C fan/425°F/Gas 7).
Prep filling ingredients. Finely slice the leeks. Peel and mince the garlic. Zest and juice the lemon. Drain and rinse the butter beans.
Cook filling base. Heat the olive oil in a large, deep, ovenproof pan over a medium heat. Add the leeks and a pinch of salt and cook for 5 minutes, stirring often, until soft and translucent. Add the garlic and thyme and cook for another minute.
Build sauce. Add the flour and cook for 1 minute, stirring. Gradually, pour in the stock, stirring to avoid any lumps forming. Add the coconut milk, miso, and nooch, if using, then season with salt and pepper. Simmer the sauce for 5 minutes, until smooth and thickened. Tip in the butter beans and spinach, stir, and cook until the leaves wilt and the beans are heated through. Add the lemon juice and zest. Taste and season with extra salt and pepper, if needed.
Top pie. Remove the pan from the heat. Scrunch each sheet of filo loosely and arrange them over the filling until they cover the top. Brush or spray with olive oil and sprinkle with fennel seeds.
Bake pie. Transfer the pan to the preheated oven and bake for 18 minutes, or until the filo is crisp and golden.
Assemble and serve. Chop the parsley and scatter over the top of the pie before serving with a salad or seasonal greens on the side