1) For the rub: mix all ingredients together. Sprinkle 2 to 3 tbsps on sliced steak, tossing to insure the meat is covered. Reserve for later use.
2) In a cast iron skillet, add flour over low heat. Brown flour, stirring occasionally to avoid burning, about 5 minutes.
3) Heat heavy 5 1/2 L cast iron pot; over medium heat, add oil. Brown seasoned meat for 2 or 3 minutes, turning once. Add onion and browned flour. Pour 225 ml of stock and stir to combine well. Add some of the greens, and then add more broth. Repeat this until there's no more broth and greens. Lower the heat and cook for 45 minutes. Add 1 tablespoon of rub and 1/2 stick of butter.
4) When the butter has melted and greens and meat are tender, transfer to a serving bowl and serve over rice.