Preheat your oven to 350°F / 180°C.
Line a baking tray with parchment paper or a nonstick mat. 2.
In a large bowl, whisk together all the dry : almond flour, psyllium husk powder, coconut flour, flax meal, baking soda, and salt. 3.
In a separate bowl, mix the egg whites, whole eggs, and buttermilk. 4.
Pour the wet mixture into the dry .
Using a mixer, process until the dough becomes thick and well combined. 5.
Add the apple cider vinegar and lukewarm water, and process just until combined. Be careful not to overmix the dough. 6.
Using a spoon or your hands, form the dough into 8 regular or 16 mini buns.
Place them on your prepared baking tray, leaving some space between each bun. 7.
Bake for 10 minutes, then reduce the oven temperature to 300°F / 150°C.
Continue to bake for another 30 to 45 minutes. Mini buns will require less time. 8.
Remove the buns from the oven and let them cool on a wire rack to room temperature before serving. Store in an airtight container for a few days or freeze for up to 3 months.