Bring all refrigerated ingredients to room temperature. Grease 12 English muffin rings.
In the bowl of a stand mixer, beat egg whites until frothy, combine eggs, oil, and lemon juice. In a large measuring cup, combine water, 1 tablespoon sugar, and yeast; let stand for 5 minutes, or until foamy.
In a medium bowl, combine buckwheat flour, tapioca starch flour, white rice flour, dry milk powder, xanthan gum, salt, flax seed, and 3 tablespoons sugar.
Add yeast mixture to the egg mixture, then slowly add dry ingredients a little at a time until completely incorporated. Mix batter on high speed for 31/2 minutes, then pour into 12 English muffin rings.
Cover bread with foil and place in a cold oven. Set a pan of hot water on a lower shelf underneath the buns. Leave for 10 minutes with oven door closed. (This will cause the buns to rise quickly.) Remove buns from oven (do not uncover) and place in a warm place in the kitchen. Preheat oven to 400°F.Buns will continue to rise as oven preheats.
Uncover buns and bake for 10 minutes to brown the top. Cover bread with foil and continue to bake bread for 5 - 10 minutes. Turn bread out onto a cooling rack.
When completely cooled, wrap tightly to maintain freshness for as long as possible. Once completely cooled these buns freeze well. Always serve buns warmed, otherwise they will be crumbly.
TIPS: If humidity is high, reduce the amount of water in the recipe to avoid over rising. Many gluten-free bakers experience the frustrating situation in which a beautiful loaf of bread deflates once removed from the oven. You will need to experiment a little to get just the right amount of water in your bread depending on the humidity in the air. If in question, use less water than the recipe calls for.