Dissolve yeast in warm water in a bowl. Let stand until yeast softens and begins to form a creamy foam, about 10 minutes. Add egg, egg white, oil, and vinegar; whisk until well combined.
Grease a 2-pound loaf pan.
Sift flour and xanthan gum into the bowl of a stand mixer fitted with the paddle attachment; mix on low speed. Gradually mix in yeast mixture. Increase speed to medium and mix until batter is smooth. Pour batter into the prepared loaf pan and smooth out. Cover with a towel and let rise in a warm place until doubled in volume, about 1 hour.
Preheat the oven to 375 degrees F (190 degrees C).
Bake in the preheated oven until the top is golden brown, about 45 minutes. Carefully tip the loaf out onto a work surface and gently tap the bottom; if it sounds hollow, it is done. Cover with a towel and let cool before slicing.