Preheat oven to 220°C (200° fan-forced). Bring a large pot of water to the boil and blanch potatoes for 3 mins. Drain well and then shake potatoes out onto a large baking tray. Drizzle with half the oil, sprinkle with thyme and season. Toss well to coat. Bake for 15-20 mins, turning potatoes at least twice, until golden brown and crisp.
In a small bowl, place peppercorns, vinegar and 2 tablespoons water. Set aside to soak for 5 minutes.
Meanwhile, brush steaks with remaining oil, season and cook in a non-stick frying pan over medium-high heat for 3-4 minutes each side or until cooked to your liking. Set steaks aside on a plate loosely covered with foil to rest for 5 minutes. Spray same pan with oil, reheat over medium heat and cook garlic for 1 minute. Add spinach and a tablespoon of water and cook for a further 2 minutes until wilted. Set spinach aside to keep warm.
In same pan, reduce heat to medium-low, add peppercorn mixture and bring to the boil. Reduce heat to low and simmer for 1-2 minutes or until liquid has nearly evaporated. Whisk stock and sour cream into pan and simmer, stirring occasionally, for 3-4 minutes or until thickened. Season with sea salt.
Serve steaks with chips, spinach, peppercorn sauce, green vegetables and extra thyme.