Heat the olive oil in a deep non-stick pan, ensuring it is no more than a third full, over a medium heat. Add the sliced onions along with the thyme sprigs, and fry gently for 15-20 mins until golden.

Tip in the potatoes and cook gently for 10 mins until tender but not falling apart. Drain well (reserve the oil to make your next tortilla – keep chilled).

Beat the eggs in a bowl and season well, then add the hot cooked onions and potatoes, and mix well to coat.

Heat the extra virgin olive oil in a 20cm cast iron or non-stick frying pan over a high heat. Pour in the tortilla mixture and swirl until the outside starts to set. Reduce the heat to medium-low and cook for 4-5 mins until starting to set – the bottom and sides should be golden and the centre loose.

Put a board wider than the pan over the top and invert the tortilla onto it. Carefully slide the tortilla back into the pan and set over a low heat.

Use a spatula to tuck in the edges of the tortilla and give it a curved look. Cook for another 2-3 mins (the centre should still be a bit runny), then turn out onto a board and leave to stand for 5 mins before serving.