Heat some of the oil and butter in a pan over medium heat. Slice the onions very thinly into rings. Fry the onion rings, stirring occasionally, for 5-7 minutes until golden and soft. Transfer to a plate.
In a second pan, heat the remaining oil and butter over medium-high heat. Finely chop the liver and add to the pan. Cook, stirring frequently, for 2-3 minutes until the liver is no longer red. Pour in the dry Marsala (roughly 100 ml) and scrape up any browned bits from the bottom of the pan. Let simmer for 1-2 minutes.
Add the cooked onions back to the liver. Season with salt, pepper, and a pinch of gingerbread spice to taste. Mix well and serve.