Dice the cleaned fillet of beef (do not chop) and place in a bowl. Then dice the shallots.
Our tip: blanch the shallots three times in boiling water. Blanching means: add the diced shallots to the water, boil for 10 seconds, strain and cool under cold water. Repeat this procedure a total of three times. This eliminates the bitter substances.
Then cut the basil into fine strips and mix with the mustard, shallots and beef.
Then hollow out the inside of the apples and finely chop the pulp of the apples and add to the tartar.
Finally, season the tartar with salt, pepper and olive oil and garnish with the walnuts.
Our tip: when serving, the hollowed apple can be filled with tartar.