800 gmchat potatoes, peeled and halved80 ml(1/3 cup) buttermilk2 tbspextra-virgin olive oil, plus extra for drizzling1 tbspwhite wine vinegarFinelygrated rind and juice of ½ lemon2 tspDijon mustard1garlic clove, finely chopped½ cupcoarsely chopped mixed herbs such as mint, flat-leaf parsley and chervil2spring onions, thinly sliced4T-bone steaks (about 250gm each), at room temperatureRough rocket salsa verde2 cups(firmly packed) rocket80 mlextra-virgin olive oil80 mlolive oil20 gmfinely grated parmesanFinelygrated rind and juice of 1 lemon1garlic clove, coarsely chopped
Boil potatoes in a large saucepan of salted water until tender (10-15 minutes). Drain, transfer to a bowl and coarsely crush with a fork or potato masher. Add buttermilk, extra-virgin olive oil, vinegar, rind, juice, mustard and garlic, season to taste and toss to combine. Just before serving, add herbs and spring onion and stir to combine.
For rough rocket salsa verde, pulse ingredients in a food processor to a coarse paste, season to taste and set aside.
Heat a char-grill pan or barbecue to high heat. Season steaks well, drizzle with oil and grill, turning occasionally, until cooked to your liking (6-7 minutes for medium-rare). Transfer to a plate to rest for a couple of minutes, then serve with potato salad and rocket salsa verde.