Line a baking sheet with a sheet of parchment paper. Grease six English muffin rings, and set them on the parchment-lined baking sheet.
Combine the sugar and warm water in the bowl of a stand mixer. Sprinkle the yeast over top. Let it sit 5 minutes.
Whisk the dry ingredients (flours, skim milk powder, xanthan gum, and salt) together in a mixing bowl.
Add the vinegar and eggs to the yeast mixture in the stand mixer bowl. With the medium paddle, beat the mixture until it's foamy.
Add the flour mixture, and beat it all on medium-low speed for 3 to 5 minutes until the batter is smooth. You might want to stop once to scrape down the sides of the bowl to make sure that all of the dry mixture has been incorporated. The batter will be thick, moist, and sticky.
Add the melted butter. (Make sure it isn't hot.) Beat another minute or two until it is well blended in.
Spread the batter into the prepared baking rings.
Smooth out the batter with an oiled spatula. Sprinkle with sesame seeds, it desired.
Allow the dough to rise for an hour in a warm room.
Bake in a preheated 400° F (204° C) oven until the buns reach an internal temperature of 180°-190° F (82°-88°), about 15 to 20 minutes.
Allow the tray of buns to cool on a wire rack. Remove the buns from the rings when they're cool enough to handle.
Slice cooled buns in half horizontally to use for hamburgers.
It's important that the water be neither too hot nor too cold, or it will destroy the yeast. Between 100° - 115°F (38° - 46°C) is just right.
Bread dough rises best in a warm room. It's really happy in 80°-90° F (27° - 32°C).
Don't overcook the buns, or they will become too dry. If you don't have an instant-read thermometer, you might want to consider getting one. It makes it easy to know when your buns or bread are perfectly done.
Store homemade gluten free hamburger buns in a sealed container in the refrigerator or freezer.