Preheat the oven to 350°F with a rack in the lower-middle position. Line a baking sheet with parchment paper.
Blend the cottage cheese, egg whites, warm water and apple cider vinegar in a blender until completely smooth.
In a large bowl, whisk together the almond flour, psyllium husk powder, baking powder and sea salt until no lumps remain.
Pour the blended mixture into the dry ingredients and mix for about 30 seconds, just until a soft dough forms. Let the dough rest for 5 minutes so the psyllium can absorb the liquid.
With wet hands, divide the dough into 6 equal portions and shape each one into a smooth dome about 3.5 inches wide. Arrange them on the baking sheet with 2 inches of space between them.
Brush the tops gently with the beaten egg and sprinkle with the sesame seeds.
Bake for 45 to 50 minutes, until the buns are puffed, golden brown and sound hollow when tapped on the bottom.
Cool completely on a wire rack before slicing in half. For the best burger experience, toast the cut sides in a buttered skillet for 1 minute.