Fill a measuring cup or bowl with 1/2 cup warm water (warm to the touch but not TOO hot). Sprinkle the yeast and inulin on top of the water, stir once then cover with plastic wrap and set it aside.
In another large mixing bowl, add your vital wheat gluten, oat fiber, lupin flour, tapioca starch or coconut flour, allulose, baking powder, xanthan gum and salt. Whisk to combine, making sure there aren't any large clumps.
Once your water/yeast/inulin mixture is frothy and bubbly and smells of beer (you know it's activated!) add it to the dry ingredients along with the 1/2 cup warm heavy cream, the whisked egg and melted butter and start stirring everything together using a spatula. Add an extra tablespoon or two of warm water only if/as needed.
Once the dough starts to become hard to stir, use your hands to knead most of the flour into the dough.
Continue to knead the dough for another 5-8min (you can do this in the bowl or on a greased and vital wheat gluten floured clean surface, I do it on greased parchment paper) or until everything is fully incorporated, the dough feels elastic and when a finger is pressed into it gently, it slowly springs back. If you are unsure if it's kneaded enough, knead for another 2-3min! It won't hurt it. (Also see my tips section for the consistency you want your dough and how to achieve it if your dough is too wet or too dry).
After you are done kneading the dough, place it into a large greased bowl and cover it with saran wrap. Place it somewhere relatively warm to rise for 1 hour (don't worry if it doesn't double in size, it will just grow slightly). (See my tips for where I find mine rises best).
Once your dough has risen, punch it down, then remove it from the bowl onto a greased surface.
Start heating your pot of oil on the stove.
Meanwhile, roll the dough out about 1/2 inch thick. Use a greased round cutter or large glass to cut circles out of the dough (twist back and forth to cut the dough more easily), then use a smaller round cutter or shot glass to cut out the center of the donuts.
Place the shaped donuts onto a parchment-lined pan. Cover them with saran wrap while you prepare the rest.
After the donuts are shaped, add the sweetener and cinnamon to a large pasta bowl and whisk together. Also set some paper towel aside for when your donuts are done frying.
Once your oil is hot, test a donut hole to see how it fries. If it browns too quickly, turn the heat down slightly or take your pot off the heat for a few minutes. If you have a thermometer then try to keep your heat between 325*F to 350*F.
You want the donuts to take a few minutes to brown on each side. Flip half-way through using a large slotted spoon or gently flip with a fork. Try to only cook 1-2 donuts at a time depending on the size of your pot.
Finished donuts should be a dark golden brown colour. Place it on the paper towel to absorb some excess oil, then move it the the pasta bowl and roll it in the cinnamon sugar mixture. Place the finished donuts on a plate. Repeat this process until all the donuts are finished. Serve warm and enjoy your Fried Keto Donuts!