Preheat oven to 120 degrees C. Line baking trays with baking paper sprayed with cooking spray.
Beat the egg whites in a bowl with an electric mixer until they form stiff peaks. Gradually beat in the sugar, adding about 2 tablespoons at a time. Beat in the salt and vanilla essence until the mixture is glossy and holds its shape. Gently and lightly use a rubber spatula to fold the cornflakes, coconut and walnuts into the meringue. Gently run the spatula through the center of the bowl, then around the sides of the bowl, repeating until fully incorporated. Drop the mixture by rounded tablespoons onto the prepared baking trays.
Bake in the preheated oven until the biscuits are very lightly browned and set, 20 to 30 minutes. Let cool completely before removing with a metal spatula; warm biscuits are very fragile.