Preheat oven to 375ºF. Grease desired pans with olive oil and line with parchment paper.
Whisk almond flour, potato starch, coconut flour, flaxmeal, psyllium husk, salt, and baking soda in a bowl until well combined and lump-free.
In the bowl of a stand mixer (or by hand), combine egg whites, olive oil, and apple cider vinegar. Add flour mixture to the egg white mixture and beat on medium-low to combine well. You are not trying to whip the egg whites.
Pour in boiling water and blend on medium-low speed for 1 minute.
Transfer batter to the prepared pan.
Crack egg in a small bowl and brush the tops of loaves.
Bake for 1 hour for large loaf or 40 minutes for small loaves.
Remove from the oven then carefully remove the loaf from the pan. Place the bread loaf back into the oven right on the oven rack. Bake until loaf forms a golden crust, about 10 more minutes.
Cool the bread completely on a cooling rack before slicing.
Store bread at room temperature in an airtight container or wrapped well with plastic wrap for up to 3 days. Or store well-wrapped in the refrigerator for up to one week and freezer for 3 months.
Not everyone agrees about flax on Passover so do your research to see if it’ll work. Otherwise, you could up the psyllium by a tablespoon or two and add a touch more almond flour instead.