Roast Fillet of Beef with Béarnaise Sauce

1 whole fillet of well-hung dried aged beef — 2.6kg (6lb) approximately

a few cloves of garlic

pork caul fat (if available)

sea salt and freshly-cracked pepper

extra virgin olive oil 

Béarnaise Sauce:

4 tablespoons tarragon vinegar

4 tablespoons dry white wine

2 teaspoons finely chopped shallots

pinch of freshly ground pepper

2 organic egg yolks

110g (4oz) butter

1 tablespoon freshly chopped French tarragon leaves