Pan sauces are easier to make than you think: our mushroom sauce gets added flavour from cooking the steak in the same pan.
1. Sprinkle steaks with salt, then season with fresh pepper.
2. Heat a large non-stick frying pan over medium-high. Add 2 tsp oil, then mushrooms. Cook, stirring occasionally, until golden brown, 5 to 6 min. Transfer to a plate.
3. Add 1 tsp oil to pan, then steaks. Reduce heat to medium. Cook until bottoms are brown, about 3 min. Flip steaks and continue cooking, 2 to 3 min more for medium. Remove to same plate as mushrooms and cover with foil.
4. Melt butter in same pan, then add flour. Stir until flour is lightly browned. Add broth, shallot and thyme, and boil gently until thickened, 3 to 5 min. Stir in reserved mushrooms and cook for 2 min, and then transfer to a medium bowl.
5. Wipe pan clean, then return to medium-high. Add remaining 2 tsp oil, then green beans. Cook, stirring occasionally, until beans are tender-crisp and brown, about 4 min. Thinly slice steak. Serve with beans and drizzle with mushroom sauce.