480 gmfinely diced ox or beef tenderloin fillet (see note)1 tbspextra-virgin olive oil3small Swiss brown mushrooms, thinly sliced¼bunch of chives, thinly slicedTo serve:grilled thinly sliced sourdough baguette and lemon cheeksLemon and sherry vinaigrette1small clove of garlic, coarsely chopped1 tspDijon mustard25 mllemon juice25 mlsherry vinegar200 mlextra-virgin olive oil
For lemon and sherry vinaigrette, combine garlic, mustard and a teaspoon of sea salt in a mortar and pound to a smooth paste using a pestle. Add lemon juice and vinegar, then stir in olive oil without emulsifying. Season to taste with freshly ground black pepper and set aside. Makes about 1 cup. It keeps for up to a week in the refrigerator.
Place ox fillet in a bowl, drizzle with olive oil and season to taste. Mix to combine then divide among six serving plates, arranging down the centre of plates.
In a separate bowl combine mushrooms and chives, drizzle with a little vinaigrette and stand for 5 minutes to lightly pickle mushrooms. Arrange over beef, drizzle with a little extra vinaigrette and serve immediately with grilled sourdough and lemon cheeks.
Note Ox is an older, more flavoursome meat than that sold as beef. At GA&S, Rob Marchetti uses 150-day grain-fed ox fillet.