Grease a 19cm square cake pan and line with baking paper. Bring the stock to the boil in a large saucepan over medium-high heat. Reduce heat to medium-low. Gradually add 1/2 cup polenta in a thin, steady stream, stirring constantly, until well combined. Cook, stirring constantly, for 5 mins or until polenta boils and thickens. Remove from heat. Stir in the butter and parmesan. Pour into the prepared pan. Set aside for 1 hour to set.
Meanwhile, place garlic, basil, rosemary and oil in a jug. Season well. Stir to combine. Reserve one-third of the oil mixture. Place steaks in a glass or ceramic dish. Pour over remaining oil mixture. Set aside for 30 mins to marinate.
Preheat oven to 200°C. Turn the polenta onto a clean work surface and cut into thick batons. Place the remaining polenta on a plate. Add polenta chips and turn to coat. Arrange polenta chips and rosemary sprigs on a baking tray and spray with oil. Bake polenta for 20 mins or until lightly golden on the edges. Place the tomatoes on another baking tray and spray with oil. Bake with the polenta for the last 10 mins of cooking.
While the polenta chips are baking, heat a chargrill on medium. Cook steaks for 2 mins each side for medium-rare or until cooked to your liking. Transfer to a plate and cover with foil. Set aside for 5 mins to rest. Thinly slice steaks.
Arrange steak on serving plates and drizzle with reserved oil mixture. Serve with polenta chips, tomatoes and salad leaves.