For microwave: Combine the butter and maple syrup in a small bowl, and microwave until the butter melts. Take the bowl out, then whisk in the powdered sugar until you have an even mixture.
For stovetop: Combine the butter and maple syrup in a small pan, and heat on medium until the butter melts. Take the pan off of the heat, then whisk in the powdered sugar until you have an even mixture.
Video
Notes
If the glaze starts to harden in the bowl while you wait for your baked goods to be ready, just give it a stir to smooth it out before drizzling.