Preheat your oven to 300°F (150°C) and line a standard loaf pan with parchment paper.

In a clean, dry mixing bowl, use an electric mixer to beat the egg whites and cream of tartar on medium speed until soft peaks form, about 2-3 minutes.

Increase the speed to high and continue whipping until stiff peaks hold, which should take an additional 2-3 minutes.

In a separate bowl, combine the sugar, salt, and tapioca flour. Whisk these ingredients together until they’re well blended.

Gently fold the dry ingredients into the whipped egg whites using a spatula until just combined.

If you’re adding color, divide the batter into two bowls. Add a few drops of food coloring to one portion and swirl gently.

Spoon the batter into the prepared loaf pan and smooth the surface with a spatula. Bake for 25-30 minutes or until golden brown.

Once baked, carefully remove the loaf from the oven and let it cool in the pan for about 10 minutes before transferring it to a wire rack.