Preheat a griddle pan or a barbecue over medium heat. once the charcoal ashes turn white, Oil the barbecue ridge.
Brush the steaks with a little oil on both sides and season with some salt and pepper.
Add the steaks on its flank or fatty edge to colour for a minute or until light colouration. This will give you a better final result.
Then, place the steaks on the pan or griddle pan and leave it for 2 minutes or until the edges are caramelised. This will allow a perfect colouration.
Turn the steaks over and cook for a further 2 minutes for rare.
Once turned, add the garlic cloves, rosemary sprigs and butter to the pan.
Let it foam and baste the steak using a spoon. Once cooked to your liking remove from the pan and set aside to settle for 2-3 minutes.
In the meantime, combine the mustard, lemon juice, salt and pepper with enough olive oil to create a dressing. Drizzle the salad leaves with the dressing and place on the serving platter.
Remove the steaks from the plate and place on a serving board with the salad leaves.
Carve each steak and serve in the middle of the table to share with the salad leaves and your favourite sides.