I found this recipe at karenscakes.com I will be trying it this weekend. I seems promising.
Of course, don’t forget the easiest of all and what my family used when I was a kid: powdered sugar glaze. Throw some powdered sugar into a bowl. Add just a bit of liquid at a time (GFCF milk, orange juice, flavoring, etc.) and mix. Make it as thick or thin as you like. You can tint this or not. Toss on GFCF sprinkles or not. Simple!
The recipe from karenscakes.com:
Meringue Powder Buttercream
1/3 cup water
3 T. meringue powder
1/2 cup shortening
5 1/2 cups powdered sugar
1 tsp. vanilla extract (use clear vanilla if you want a pure white icing)
1/4 tsp. almond extract
Beat water and meringue powder until stiff peaks form. Add shortening, sugar, and extracts and whip for 3 minutes. Store well covered.
Note: I have had a lot of problems with tiny lumps in this icing, which prompted me to experiment to see if I could eliminate the problem. My theory is that the lumps were being caused by the meringue powder mixing with the water and then drying on the sides of the bowl. So, what I came up with is this:
Sift half of the powdered sugar with the meringue powder, and place in the bowl of a large mixer. Turn on mixer (use whip attachment) and, while mixing the sugar, slowly stream in the water. Let it mix, until everything is incorporated. Avoid scraping the bowl down if you can. When stiff peaks form, add flavorings and mix well. Then add remaining powdered sugar and shortening and whip for 2-3 minutes more. Hopefully you will have a lovely, lump-free icing!