Preheat oven to 325°F. Use middle rack and remove any racks above as bread will expand while baking.
Generously butter a loaf pan with butter. Use a ceramic pan for best results- the bread will cook evenly without sticking to the pan.
Beat egg whites until stiff peaks form – a hand mixer on high works well.
Add ½ cup of whey protein and the yolks. Blend gently on low speed just until fully incorporated. The batter will be fluffy.
Pour batter into a loaf pan/dish and place in oven. Bake for 40 minutes.
Remove and allow to cool completely. The loaf will sink to a normal height.
Once fully cooled, release from the dish, slice, and serve.
Wrap leftover bread in an air tight zip top bag. Leftovers will keep in the fridge for a few days.
To Reheat: Heat a skillet to medium-high and add ghee or butter, sear bread slices in skillet until lightly toasted on each side, about 30 seconds per side. Do not overheat.