Cooking Method
Bring a pot of water to the boil, then reduce to a strong simmer. Add the eggs and cook for 8 mins. Transfer immediately to an ice bath to stop the cooking, then peel and separate the whites and yolks. Chop the egg whites into small cubes.
In a large mixing bowl, whisk the egg yolks with white wine vinegar and Dijon mustard until smooth. While whisking continuously, slowly stream in the olive oil to emulsify the sauce. Stir in cornichons, capers, and fines herbs, then season with salt and pepper. Gently fold in the chopped egg whites and set the gribiche sauce aside.
Butter the brioche and toast in a pan until golden on both sides. To assemble, spread a generous layer of gribiche sauce over one slice of toast, pile on the shaved beef tongue, and add more sauce if desired. Top with the second slice of toast, cut in half, and serve.
