Preheat the oven to 375°F and set an oven rack in the upper-middle position. Line a 13x18-inch baking sheet with parchment paper.
In a large bowl, whisk together the flour, baking powder, and salt. Add the yogurt and, using a fork, mix the ingredients just until they form a shaggy, crumbly dough. Using your hands, knead the dough until it forms a slightly tacky mass and no crumbs remain (do not overwork the dough; this process shouldn't take more than a minute or so).
Place the dough on a lightly floured work surface and form it into a flat disc. Divide the dough into 6 equal pieces (if you want to weigh them, they should be about 92 grams each). Roll each piece of dough into a ball (the dough will have a slightly uneven and craggy appearance, similar to biscuit dough -- that's okay). Use your finger to poke a hole in the center. Lightly flour your hands, and gently pull and stretch the dough into a bagel shape until the center hole is about 1-1/2 inches in diameter and the bagel is just shy of an inch tall. Repeat with the remaining pieces of dough, sprinkling with more flour as necessary.
Arrange the bagels on the prepared baking sheet. In a small bowl, beat the egg with 2 teaspoons of water. Brush the bagels with the egg wash and sprinkle with the toppings, if using.
Bake for about 25 minutes, until golden. Let the bagels cool on the baking sheet for at least 15 minutes before slicing. Before serving, slice the bagels in half and toast.
Make-Ahead/Freezer-Friendly Instructions: The bagels will keep in an airtight container in the refrigerator for two days; freeze for longer storage. For best results, slice and toast the bagels before serving.