Method
Pour 1 tbsp of the oil into a 20cm non-stick frying pan set over a medium heat. Finely slice the onion, then, when the oil is shimmering hot, add to the pan and stir-fry for 10 minutes or until soft and golden. Transfer to a plate.
Add the remaining 1 tbsp oil to the pan and set over a low-medium heat. Add the potatoes along with their butter and cook gently for 5 minutes, turning occasionally, or until cooked through but not browned.
Meanwhile whisk the eggs in a mixing bowl. Chop the herbs and add to the bowl, then season generously.
Turn down the heat to low, then return the onions to the pan along with the ham hock. Pour in the egg mixture and cook for 2-3 minutes, occasionally lifting the egg with a spatula so the uncooked mixture on top runs to the bottom of the pan. Cook for a further 5 minutes or until almost set.
- Release the sides of the tortilla with a palette knife, then invert onto a plate (see Know-how). Drizzle a little more of the oil into the pan if necessary, then slide the tortilla back into the pan along with any runny egg that might have leaked out. Heat for another 3 minutes or until cooked throughout. Turn out onto a board or plate and slice into wedges to serve.