Heat oven to 200C/180C fan/gas 6.
Using a large frying pan, soften the onions
with 1 tbsp olive oil and some seasoning.
Cook over a low heat for 20 mins or until
golden and caramelised.
Place the potato slices, 3 tbsp olive oil
and seasoning onto a large baking tray
or 2 small ones and toss them around.
Bake for 15 mins until potatoes are soft,
but not brown.
Mix the eggs in a large bowl with more
seasoning. When the potatoes and
onions are done, toss them in and mix
well. Add the remaining 1 tbsp oil to a
20cm frying pan, warm it and pour in the
egg mixture. Allow to cook slowly over a
low heat for 20-25 mins.
When nearly all the liquid egg is gone,
you will need to flip it over. Place a plate
on top of the pan and invert the tortilla,
holding the plate firmly while doing so.
Slide the tortilla back into the pan and
cook for another 3-4 mins. Alternatively,
if you aren’t too confident about flipping
and your pan is ovenproof, place the pan
under the grill for a few mins until the
top is done. Serve cut into wedges,
warm or at room temperature.