Preheat your oven to 400°F. Line a large rimmed baking sheet with unbleached parchment paper and set it aside.

In a large bowl, place the flour blend, xanthan gum, baking powder, and salt, and whisk to combine. Add the yogurt, and mix until combined.

Depending on the moisture content in your yogurt, the dough may still not hold together fully. If necessary to bring the dough together, add the egg white (or a bit more yogurt) by the teaspoonful.

Mix to combine until the dough holds together well.

Turn the dough out onto a very lightly floured surface and knead it with clean hands until it’s a bit smoother. Divide the dough into 6 equal portions (each a bit more than 2 ounces in weight).

Working with one piece of dough at a time, roll each into a ball between your cupped palms and/or by rolling on the lightly floured surface. Add a bit more flour as necessary to keep the dough from sticking. Even when shaped, the dough will seem somewhat uneven.

Press each round of dough into a disk about 1/2-inch tall and, with a floured forefinger, create a hole in the center and rotate the dough to increase the size to about 1-inch. Reshape the dough around the hole if necessary.

Place the shaped pieces of dough about 2 inches apart on the prepared baking sheet. Brush generously with the optional egg wash and top with the optional toppings.

Place the baking sheet in the center of the preheated oven and bake, rotating once during baking, until the bagels are puffed and golden brown all over, about 22 minutes.

Allow to cool briefly on the baking sheet before slicing and serving.

Leftovers can be sliced and stored in a sealed container at room temperature for up to 2 days (to maintain moisture, add a moistened paper towel to the bag) or sealed in a freezer-safe container for longer storage.