Pre-heat the oven to 355F / 180C.
Now prepare the pastry. Lightly brush or spray an 8" loose-bottomed baking pan with olive oil, then drape a sheet of filo pastry in the centre of it at an angle, with about half of it hanging over the edge. Repeat with the other 4 sheets of pastry, rotating the pan as you go so that the whole of the bottom of the pan and the sides are covered with pastry. Brush lightly with olive oil between each layer.
You’ll see that some of the ingredients are optional. The tomatoes, onions and herbs add a little something, but really just the spinach and cheese are essential!
Please bear in mind that I've not included the brushed-on olive oil in the nutrition facts below!
It doesn't matter if you don't have an 8" baking pan. Use any round baking pan you have - as long as it isn't too much bigger or smaller - and you'll be fine!