Here is the secret to making petits fours . . . fondant, a candy-like glaze!
In a medium saucepan set over medium heat, add the sugar, corn syrup, glycerin, salt, cream of tartar and water. Cook to 226Fº. Pour into a large stainless steel mixing bowl. Cool to lukewarm(just about 5 - 10 minutes).
Add the powdered sugar. Whisk until any lumps are gone and it is a consistency to pour.
Set the bowl of fondant over a saucepan of hot water, about 2" depth of hot water, over low heat. This will keep the fondant from cooling off and hardening.
Place the small cakes on a wire rack. Set the wire rack over the bowl of fondant.
Ladle the fondant over the cakes. Once should be enough. If the fondant is too thin, ladle a second coat onto them. Add any decoration now, before they dry.
Set aside to dry, an hour should be plenty of time.
Gently, slide a spatula under one petit four at a time and place on serving tray.