Preheat the oven to 200°C.
Whisk together the 25ml of groundnut oil, the five-spice, cornflour and seasoning for the steak marinade. Rub the steaks in the marinade, then cover and chill as you prepare the sauce.
Heat the groundnut oil for the sauce in a medium frying pan over a moderate heat. Sweat the shallot and garlic for 2-3 minutes, stirring occasionally. Add the peppercorns, then de-glaze with the dry sherry. Stir in the crème fraîche and bring the sauce to a simmer. Season to taste with the soy sauce, then remove from the heat and set to one side. Remove the steaks from the fridge to let them come up to room temperature.
Heat a large heatproof frying pan over a medium-high heat until hot. Sear the steaks until golden brown on the outside, then transfer to the oven to finish cooking. Roast for 5-8 minutes depending on desired doneness, then remove and rest them on a plate covered loosely with tin foil.
Meanwhile, heat the groundnut oil for the spinach garnish in a large frying pan set over a moderate heat. Wilt the spinach, stirring all the time, for 1-2 minutes. Season to taste, then spoon into the centre of serving plates. Thinly slice the steaks and lay across the spinach.
Reheat the sauce at the same time and spoon on top of the steak. Serve immediately.
For top tips on protecting you and your family when preparing raw meat and poultry, visit Food Safety in the Home.