In a bowl, add your batter ingredients and whisk to blend.
Add the gluten free beer. I used a measuring glass because you only need 12 ounces of gluten free beer, but my can had 16 ounces in it.
You can also put it all in a Vitamix or blender to make sure there are no lumps!
Pour the beer into the dry ingredients. Whisk until your batter is a little runny but it should be a thick runny.
If using a Vitamix, add all ingredients and blend until smooth. Allow the batter to sit for 10-15 minutes in the refrigerator.
Peel your onions and cut them horizontally to remove both ends.
Gently separate the onion into rings. Pressing down on the more narrow end makes it easier and you won't rip the onions this way.
While the batter is chilling in the refrigerator, heat oil in your 12-inch cast-iron skillet or Dutch oven. I tend to use a Dutch oven if I am frying inside. The sides are higher so there is less mess. If I am frying outside and using the side burner on my grill, I use my cast-iron skillet. You will want your oil to be around 375º F.
Carefully dip the onion rings into the batter. Be sure the batter coats all areas of the onion ring.
Gently lift the onion ring and shake off the excess batter.
Drop an onion ring into the hot oil. I cook 3-4 at a time but make sure there is a lot of space around each onion ring.
Allow the batter-coated onion rings to cook for 1 ½-2 minutes on each side. It is easiest to cook the onions in small batches so that none get overcooked.
Quickly move the fried onion rings to a paper towel-lined plate so the excess oil can be absorbed. Continue until all of the onion rings are fried.