Powdered sugar itself holds the clue to what you can substitute for it -- the sugar is made from granulated sugar and small amounts of cornstarch, two ingredients you can use to make glazes for donuts. If you have run out of powdered sugar to make a glaze or if you just want to expand your culinary repertoire, there are other ways to give your donuts the same smooth and shiny coating that powdered sugar provides.
Pure and Simple
While simple syrup provides the sweet base for cocktails, it's also a fine substitute for powdered sugar as a glaze for donuts. Made by boiling equal parts water and either sugar or honey until the sugar dissolves, simple syrup thickens to any consistency you want depending on how long you boil it. You can also flavor the syrup by using green tea, fruit juice or any other liquid instead of water for unique glazes.
A Natural Thickener
Cornstarch thickens liquids to a clear, shiny finish and gives you more control over your glaze's sweetness since the starch itself is flavorless. Boil any liquid, from juice to coffee to cola, adding 2 teaspoons of cornstarch for every 2 cups of liquid, and add sugar to taste. Simmer the mixture for a minute or two until it thickens, then flavor it with a few teaspoons of liqueur or flavored extracts.
Come As You Are
With just a few seconds in the microwave, jams and jellies transform themselves into sweet glazes for drizzling on donuts or for coating them entirely. Honey and maple syrup also give donuts a shiny coat, although honey may need some thinning in the microwave if it has thickened. Pour honey from a plastic container into a microwave-safe one before heating. And for the simplest glaze of all, use ice cream toppings from the grocery store in flavors from chocolate to pink lemonade.
Rich Chocolate Ganache
Made with chocolate and heavy cream, ganache comes out as thin or thick as you want, depending on how much cream you add. Heat the chocolate and cream together with any additional flavoring agents, then let the mixture cool before pouring it over donuts. Flavors that pair well with chocolate and that will deepen the flavor of the glaze include liqueurs like orange-flavored Grand Marnier liqueur, espresso or strongly-brewed coffee, brandy, rum and vanilla.