Preheat your oven to 375°F (190°C). Line a baking sheet with parchment paper.
In a large bowl, whisk together the almond flour, coconut flour, psyllium husk powder, baking powder, and salt until evenly combined.
Add the eggs and melted butter to the dry ingredients. Stir until a thick batter forms. Pour in the hot water and mix quickly until a firm but slightly sticky dough comes together. Let the dough rest for 2 minutes so the psyllium husk fully absorbs the moisture.
Divide the dough into 6 equal portions. With damp hands, shape each piece into a smooth, slightly flattened round about 3 inches wide and place on the prepared baking sheet, spacing them about 2 inches apart.
Brush the tops lightly with a little water and sprinkle sesame seeds over each bun, pressing gently.
Bake for 25 to 30 minutes, until the buns are golden brown and sound hollow when tapped on the bottom.
Transfer to a wire rack and let them cool completely before slicing in half. These buns hold together perfectly for burgers and are even better lightly toasted on a skillet before assembling.
