Grate or shred the frozen stick of butter and transfer it back to the freezer until time to add it to the batter.
Reduce speed to low and stir in the yolk or whole egg powder and frozen butter shreds, just until combined.
Spread the batter into the large parchment paper lined loaf pan.
Remove the loaf from the oven and allow to cool in the pan on a wire rack for about 10 minutes.
Find the recipe for the Egg White Bread Dry Mix here: http://indigonili.com/egg-white-bread-mix/
You can find this recipe with all of the ingredients listed out individually here: http://indigonili.com/next-level-butter-bread-keto-egg-white-bread/