Cover a baking rack with cooking paper. Set aside.
In a large mixing bowl, using an electric whisk, whisk the egg white until it forms some bubbles on the sides - about 30 seconds.
Add the cream of tartar and keep whisking on high speed until a stiff peak forms. Set aside.
In a food processor with the S blade attachment place the ripe avocado flesh.
Process until smooth and creamy. You may have to stop the food processor every 20 seconds, scrape down the side of the bowl with a spatula, and process again. You want a creamy avocado puree with no lumps.
Place the creamy avocado puree onto the fluffy egg white.
Add the almond meal, baking soda, and psyllium husk.
Using a spatula or wooden spoon, gently combine all the ingredients, rubbing the fluffy egg whites with all the other ingredients. Don't go too fast to keep the mixture light and fluffy like for a souffle.
Keep stirring until all the ingredients are coming together and no more lump appears. You should obtain a fluffy batter with a pale green color.
Spoon the batter onto the cookie rack covered with cooking paper. You must evenly split the batter into 4 buns.
Use the back of your spoon to flatten the batter and shape regular round buns.
It is optional but you can sprinkle some sesame seeds on top of each bun before baking. Usually, 1/4 teaspoon per bun is enough.
Bake at 320°F (160°C) for 15 minutes or until the sides are slightly golden and the center is set.
Cool down on a rack for 10 minutes and use it as regular hamburger buns.
Storage: I highly recommend eating the buns straight away after baking. Although you can rewarm the buns in a toaster for 30 seconds the next day, they would lose the light fluffy texture.Psyllium husk: don't use Metamucil fiber supplement in my recipes, this is not the same product as whole psyllium husk fiber. Metamucil is a husk powder that is not suitable for baking keto bread. It will turn food dry, purple, or blue.