In a medium saucepan, combine the condensed milk, egg yolks, ground walnuts, and butter. Cook over medium heat (large burner), stirring constantly, until mixture has thickened and bottom of the pan starts to show through when stirred (about 5 minutes). Remove from heat and stir in the vanilla.
Pour cooked mixture into a greased dish and let cool on a rack. Lightly grease hands with butter. Roll candies into 1 tablespoon balls. Then, pressing between two of your fingers, shape into slightly elongated, oval shaped treats and finish by pressing down to flatten the top. Set aside on a lightly greased plate or surface.
To give the walnuts a golden color effect, line a baking sheet with parchment paper, arrange 20 walnuts in one single layer and spray each one of them with the edible gold food spray, then let color set at room temperature.
To prepare the "fondant" glaze, place the powdered sugar, milk, and lemon juice in a heat-resistant bowl. Whisk until obtaining a homogeneous mixture. Place bowl in a larger baking pan filled with boiling water (about 2 inches). Then, continue to whisk mixture until sugar has melted. With the aid of a fork, dip each camaféu de nozes into the "fondant" glaze, letting the excess drip off.
Place shelled walnut carefully on top well before the glaze has set. Place treat(s) on a lightly greased surface or baking sheet. If the fondant gets too thick, add a few drops of milk under desired consistency and if too thin add powdered sugar.
Once glaze has set, carefully trim off excess glaze with a knife and transfer each camaféu de nozes to a bonbon cup.