Preheat the oven to 300°F Heat 2 tablespoons of the oil in a large cast-iron pan, toss the meat in the flour, season well with salt and black pepper, then add to the hot oil with the bay leaf and stir.
Cook, stirring occasionally, for 8–10 minutes, or until the meat is no longer pink, then add the butter and cook for 5 minutes, or until the meat is golden. Remove with a slotted spoon and put to one side.
Add the remaining oil to the pan, then add the onions and cook over a low heat for 6–8 minutes, or until soft. Add the orange zest, raise the heat a little, then add the orange juice and stir to loosen all the sticky bits from the bottom of the pan.
Stir in the anchovies, then add the wine and simmer over a high heat for 2 minutes. Stir in the mushrooms, add the stock and thyme, and season with salt and black pepper. Return the steak to the pan, cover with a lid, then put in the oven to cook for 2 hours, or until the meat is meltingly tender.