Put 425ml water and a large pinch of salt in a heavy-based pan and bring to the boil. Slowly whisk in the polenta, stirring continuously. Bring back to the boil and simmer, stirring all the time, for 2-3 minutes until thickened. Remove from the heat and stir in the garlic, half the parmesan and half the black pepper.
Beat the polenta for 5 minutes to reduce the temperature, then spoon on to a board lined with clingfilm and shape to a rough 25 x 8 cm rectangle. Leave to cool for 10-15 minutes until only slightly warm, then place in the fridge for 1 hour to cool completely.
Preheat the oven to 200ºC/gas mark 6. Cut the cold polenta into chunky chips. Place the chips on a baking sheet and sprinkle over half the oil, turning them to coat. Bake for 15 minutes, turning once, then scatter over the rest of the cheese and bake for a further 8-10 minutes until crisp and golden.
Just before the chips are cooked, heat a cast-iron griddle pan until very hot. Brush each steak with the remaining oil and sprinkle with the remaining black pepper. Cook the steaks in the pan over a high heat for 1-2 minutes on each side until just seared. Remove from the pan, cover and leave to rest for a few minutes. Add the cherry tomatoes to the pan and cook over a high heat for 1-2 minutes until just softened and lightly charred.
Sprinkle the basil over the cherry tomatoes and serve with the steak and polenta chips.