Put a frying pan with ½ tbsp olive oil over a high heat. Add the runner beans and fry for 2 minutes. Add ½ tsp lemon zest and 1 tsp lemon juice. Season, mix well and remove from the heat. Set aside and keep warm.
Return the pan to the heat and add 1 tbsp olive oil, followed by the garlic. Cook for 2 minutes, then stir in the cumin and paprika. Add the cannellini beans and remaining zest and juice. Season generously, remove from the heat and mash roughly. Keep warm while you cook the steak.
Season the steak on both sides, adding more black pepper than you would usually. Heat ½ tbsp olive oil in a frying pan over a high heat until smoking hot. Add the steak and butter and cook for 2-3 minutes on each side or until cooked to your liking. Remove from the pan and leave to rest for 5 minutes.
Return the pan to a medium-high heat, add the stock and bring to the boil. Boil until reduced by half, then add the cream and heat through. Add plenty of black pepper. Serve the steak, runner beans and mash with the pepper sauce on the side.