Special equipment: a Yorkshire pudding tin or muffin tin
For the fillet of beef: To marinate the beef, mix the treacle with 3 1/2 ounces water. Put the beef in a container and cover with the treacle mixture. Leave to marinate in the refrigerator for 24 hours, turning occasionally.
When you are ready to cook, remove the beef from the marinade, pat dry and bring to room temperature. Place the marinade in a saucepan and cook over medium-low heat until the liquid has reduced by half. Season with salt and pepper.
For the Yorkshire puddings: Mix the eggs and milk together in a jug. Put the flour in a bowl and then slowly and gently whisk in the milk and egg mix. Don¿t over whisk-- lumps are okay. Rest the mixture at room temperature for at least 4 hours.
Place an oven rack in the bottom position of the oven and preheat to 130 degrees F (or the lowest possible setting on your oven).
Heat a little of the vegetable oil in a large skillet set over high heat. Add a knob of butter and brown the beef all over. Place the beef in a roasting pan and transfer to the bottom rack of the oven and cook for 45 minutes (or longer if you prefer your meat well cooked).
Remove the beef from the oven and brush with the reduced marinade. Cover and set aside to rest.
To make the roast potatoes, place a wire rack over a roasting pan. Bring a large pan of salted water to a boil. Add the potatoes and cook until soft on the outside. Drain and let them steam dry on the rack.
Preheat the oven to 400 degrees F.
Add a little of the vegetable oil to a roasting pan and place in the oven to heat. When the oil is hot, add the dry potatoes and stir gently to coat in the oil. Roast, turning occasionally, until crisp and brown, about 40 minutes.
For the Yorkshire puddings: Keep the oven at 400 degrees F. Add a little vegetable oil to each cup of a muffin tin or Yorkshire pudding tin and place in the oven to heat. When the oil is hot and the Yorkshire pudding batter is rested, fill each cup of the muffin tin and bake until risen and golden brown, 15 to 20 minutes.
Just before serving, heat the remaining knob of butter in a saucepan. Add the spinach and cook just until wilted. Season with salt and freshly ground black pepper.
To serve, heat the red wine sauce or gravy. Slice the beef and add to the serving plates with the sauce, spinach, roasted potatoes and Yorkshire puddings.
Popular in English cooking, black treacle is a sweet byproduct of the sugar refining process. You can find it at some specialty food stores and online markets.