Make the sauce base. Scoop out egg yolks into a medium bowl and mash well with a fork. Season the yolks with a good pinch (about 1/2 teaspoon each) Kosher salt and black pepper. Add mustard and vinegar, mashing to incorporate. Then slowly drizzle in the oil and continue whisking with the fork until incorporated.
Add texture. Stir in shallots, capers, and cornichons. Finely chop the egg whites and fold into the sauce.
Stir in herbs. Just before serving, stir in chopped tarragon and parsley. Season to taste with additional salt and pepper.
Notes
Shop this recipe: Visit our shopto browse quality Mediterranean ingredients, including the olive oilused in this recipe.
Make Ahead: Sauce gribiche can be made up to 2 days ahead. Cover and chill. Bring to room temperature before using.