Heat the butter and 2 tbsps olive oil in a pan over a medium heat. Add the spinach or wild garlic, season with salt and pepper then cook gently for a couple of minutes until soft, stirring occasionally.
Remove from the pan, cool slightly then gently squeeze to get rid of any excess water. Place on a board, chop roughly, then transfer to a bowl.
Crack the eggs into the bowl and gently mix together along with the oregano and jamon ( if using). Check seasoning.
Place a large frying pan over a medium high heat. When hot, add 2 more tbsps of oil and swirl around the pan. Cook in the same way as the Courgette Tortilla from the same book, using the remaining olive oil.