Preheat your oven to 350°F (175°C).
Line a baking sheet with parchment paper.
In a mixing bowl, add the 3 egg whites and beat them until stiff peaks form.
In another bowl, whisk together the whole egg and hot water until well combined. Gently fold the beaten egg whites into the wet mixture.
In a separate bowl, combine the almond flour, coconut flour, psyllium husk powder, baking powder, and sea salt.
Gradually add the dry mixture to the wet ingredients. Use a spatula to fold everything together until it forms a dough-like consistency.
Using your hands, shape the dough into buns.
If desired, sprinkle some sesame seeds on top of each bun.
Place the shaped buns on the prepared baking sheet and bake for 25-30 minutes, or until golden brown and firm to the touch.
Once baked, let the buns cool on a wire rack before slicing.