Peel, dice and rinse the potatoes. Place in a pan of cold salted water, bring to the boil and cook until the potatoes are tender.
Peel the garlic cloves, cut in half and remove the green stem. Place the rocket, garlic, pine nuts, parmesan and 100ml olive oil in a food processor and blend to a smooth paste.
Pass the cooked potatoes through a moulis to obtain a smooth mash and then add the milk, butter and rocket pesto. Season with salt and pepper.
Preheat the oven to 220°C.
For the sauce vierge: peel the tomatoes, cut into quarters, remove the seeds and then dice the flesh. Finely slice the spring onions. Pick and chop the parsley.
Mix the tomatoes, spring onions and parsley with 100ml olive oil, the white balsamic vinegar, salt and pepper. Set aside until ready to serve.
Season the fillet steaks with salt and pepper.
Heat a frying pan to hot and add a little olive oil. Colour the steaks on both sides and then remove from the pan and place on a baking sheet. Transfer to the oven and finish cooking for 4 to 5 minutes.
Plate the pesto mash using a stainless steel serving ring. Place the steak on top and finish with a generous spoonful of the sauce vierge.
«The sauce vierge can also be made using shallots instead of spring onions and basil in place of parsley.»