Leave the butter out of the fridge until it has a pasty texture.
Chop the black truffle and mix it with the butter.
Line an airtight container with cling film, put butter inside and leave it in the fridge for about 5 days.
For the tartar, chop the beef tenderloin into small pieces with a knife.
Then, season the sirloin with salt, pepper, oil and a dash of brandy.
To serve, spread a little butter on the toast and put a little tartar on top.
Finally, add the black truffle cut into strips on top of the sirloin and toast.
Bon appetit!
