Preheat the oven to 400ºF (200ºC).
Grease a sheet pan with olive oil then lay the sliced potatoes onto the tray. Season with more olive oil, salt and pepper then place into the oven until soft and golden – around 25 minutes. Remove and allow to cool.
Starting the night before, melt the butter and a large splash of olive oil in a wide bottomed pan and saute the sliced onion until softened and golden brown – around 15 minutes. Place into a bowl and set aside to cool.
Tip the bag of spinach into the pan that the onion was sauteed in and allow to wilt. Place into a sieve over a bowl to cool so that any excess water can drain away.
Once they are all cooled, cover and place in the fridge overnight.
The next morning, preheat the oven to 375ºF and grease a baking tray with sides.
Mix the eggs in a jug and season with salt and pepper.
Lay the potatoes onto the bottom of the tray then top with the spinach and onions.
Pour over the beaten eggs. If using, sprinkle with the cooked bacon.
Now place in the oven to bake until the eggs are completely set and the fillings heated through, around 20-30 minutes.
This is where you can sit back and relax with your coffee!