• 2 ounces (½ stick) butter, melted, for the waffle iron

Dry Mix

• ½ cup oat bran
• 1 cup oat flour
• 2 cups all-purpose flour
• 1 tablespoon baking powder
• 1 teaspoon kosher salt

Wet Mix

• 2 cups cold whole milk
• 4 eggs, separated
• ½ cup maple syrup
• 2 teaspoons pure vanilla extract
• 1 tablespoon sugar

1. Turn the waffle iron to its highest setting. Even if you don’t usually heat it this high, these waffles come out best when cooked at high heat.
2. Pour the oat bran into a small bowl. Bring 1 cup of the milk to just shy of a boil. Add the hot milk to the oat bran and stir, then set aside to soften while you gather the rest of the ingredients.
3. Sift the dry ingredients into a large bowl, pouring back into the bowl any bits of grain or other ingredients that may remain in the sifter.
4. Put the egg whites into the clean bowl of a standing mixer and the yolks into a medium bowl. Add the maple syrup and vanilla to the egg yolks and whisk until thoroughly combined.
5. Add the remaining 1 cup of milk to the oat bran—the cold milk will cool the lingering heat of the bran. Pour the oat mixture into the maple syrup mixture and stir to combine.
6. Using a spatula, add the wet ingredients to the dry ingredients and gently combine. The batter will still have fine lumps throughout; resist the urge to mix them in.
7. To whip the egg whites, attach the mixing bowl and the whip to the mixer and turn the mixer to high speed. As the whites whip, they will become frothy and begin to increase in volume. Add 1 tablespoon sugar. Next they will turn thick but very soft. Continue whipping until they are fluffy and glossy and hold their peaks, like clouds or cotton candy, about 3 minutes total. If they are overwhipped, they’ll crack and look mealy. If that happens, throw them out and start over.
8. Scrape half of the egg whites into the batter, stirring and folding gently so as not to deflate the air in the whites. Add the remaining half of the egg whites, and fold gently to combine. The egg whites should be entirely incorporated into the batter and the batter should be quite fluffy.
9. This light batter needs to be griddled on the waffle iron just as soon as you finish mixing it; it will deflate quickly if left to sit, chilled or otherwise.
10. Brush the waffle iron generously with butter. Using a ladle or measuring cup, scoop ½ cup of batter onto the spaces of the iron. Promptly close, and listen for the iron to sigh as the batter begins to cook. The smell wafting from the iron starts out like a freshly kneaded loaf of bread, then becomes toasty. Remove the waffle when the indicator light shows that it is done, or when a quick peek shows that it has turned a dark golden-brown, 4 to 6 minutes. Remove the hot waffle with a fork, and repeat with the remaining batter.
11. These waffles are best eaten hot, right off the iron, with a thin slab of butter melting on top and maybe a bit of jam.