Flat iron steak in red wine marinade

Flat iron steak - 500g (or thereabouts)

Red wine - 150ml (I used cheap Cabernet Sauvignon)

Garlic - 2 cloves (crushed or chopped very small)

Rosemary - 1 tsp (finely chopped fresh rosemary)

White pepper - 0.5 tsp (you can also use ground black pepper)

Salt -