Spinach Casserole

I found this recipe in the book "The 4-Ingredient Vegan" by Maribeth Abrams, and as the name suggests, it is a simple dish, with few ingredients. If you want to jazz it up a bit, I suggest adding some chopped mushrooms and maybe some herbs and spices. Chilli powder comes to mind, but maybe that's just me?
This recipe is NOT gluten free, alas, as I have yet to find gluten free phyllo pastry.

What you will need:
6 potatoes, peeled and cut into chunks
600g (approx. More if you like) chopped, frozen spinach
6 tbsp nutritional yeast flakes
1/2 tsp salt
16 sheets of phyllo dough ( I used the Antoniou brand, which is available in supermarkets.)
spray on cooking oil

Method:
Boil a pot of water over high heat and add potatoes. Cook for about 10 minutes or until fork-tender.
Drain and return to pot. Mash.
Thaw spinach according to packet instructions and then add to potatoes. Also add nutritional yeast flakes and salt, and stir.
Preheat oven to 190 degrees Celsius. Spray a large baking dish with olive oil.
Place a sheet of phyllo on the bottom of the dish and spray with oil. Repeat process for a total of 8 sheets.
Then spread the potato filling over the phyllo and lightly pack it in and smooth it out on top.
Lay a sheet of phyllo over the top of that and spray with oil. Repeat the process for a total of 8 sheets.
Spray the top with oil and bake for about 30-40 minutes, or until the top is golden brown and flaky.