Preheat the oven to 350°F.
Mix the dry ingredients in a large glass bowl.
Add egg whites and vinegar and combine well.
Gently pour in boiling hot water while vigorously mixing with a wooden spoon or or beating with a hand mixer. Do not over-mix the dough.
Cut the dough into six equal pieces.
Moisten hands with a little olive oil and shape the dough into balls. Place on a baking sheet lined with parchment.
Brush with egg wash and sprinkle seeds if you're going to use them.
Bake for 50-60 minutes. They're done when they have a golden brown color, and when you hear a hollow sound when tapping on the bottom of the bun.
Serve with butter as is or use them for burgers, sandwiches, and whatever else you’d like. They freeze really well and can be defrosted, toasted in a toaster or a griddle pan. Put it in the oven at 350°F on a baking sheet to make it crusty for 4-5 minutes for eating with soups and dipping and soaking sauces.