In a mixing bowl, whisk together the flour(s), baking powder, and salt.: Close your eyes and smell the dry ingredients; there is a clean, faintly toasty scent from the flours and a mineral brightness from the kosher salt . Whisking aerates the mixture, which helps the baking powder distribute evenly so every bite rises consistently. A common mistake is to skip thorough whisking, which can leave pockets of leavener that create uneven texture. If you see clumps, break them up with the whisk or a fork so the dough mixes uniformly.
Make a hole in the center, then add the Greek yogurt. With a spoon or small rubber spatula, stir until the mixture forms a shaggy dough.: As you press the Greek yogurt into the well, notice how it binds the dry mix into a shaggy mass, glossy where the dairy meets flour. Using a spatula keeps your hands cleaner and prevents overworking the dough, which could make it tough. The why is simple, the yogurt hydrates without excess liquid, giving protein and a tender crumb. Avoid adding extra yogurt unless the mixture is crumbly and refuses to come together, which would indicate your flours are unusually dry.
Turn the dough out onto a lightly floured work surface. Knead it for 1 to 2 minutes, until it forms a smooth dough (add a light dusting of flour to your hands and the counter if the dough is too sticky to handle).: Feel the transformation under your palms as the shaggy mass becomes cohesive and smooth, slightly tacky but not sticky. Gentle kneading develops enough gluten to give chew, while keeping the interior tender. A common pitfall is overflouring; adding too much all-purpose flour will dry the dough and make the final bagels dense. Instead, sprinkle flour sparingly and stop kneading once the surface looks even and springs back when pressed.
Divide the dough into 4 equal sections. Roll each piece into a ball, then out into a rope that is about 8 to 9 inches long and 3/4-inch thick. Connect the ends of the rope to form a bagel shape, pressing lightly to seal. Repeat with the remaining sections.: Rolling the dough into ropes lets you gauge consistency; a smooth rope with an even thickness will bake uniformly. When you join the ends, press lightly so the seam holds during cooking but does not create a hard ridge. You should hear a soft squeak as you shape them, and the surface will look taut. If seams open during shaping, dampen the edges slightly with water and press again. Avoid over stretching which can cause thin spots that puff unevenly.
If using toppings, place the bagels on a parchment lined baking sheet, then brush the tops with the egg wash so the seasonings stick. Sprinkle with your desired toppings.: The egg wash creates a glossy, brown finish and acts like glue for toppings. Brush with a light hand to avoid saturating the dough, then sprinkle seasonings so they adhere evenly. You will notice the toppings sink slightly into the wash, which helps them toast rather than blow off in the Air Fryer . A mistake to avoid is overloading toppings, which can prevent the crust from browning and make the surface soggy.
Arrange the bagels in a single layer in the air fryer basket, ensuring they do not touch (you may need to cook in batches)—for easy transfer, I remove my air fryer basket insert, place two bagels on top, then lower them in (note this only works with the first batch, as the insert will be super hot later on). Air fry at 350°F for 8 to 10 minutes, until the bagels are golden brown on top and at the sides.: In the hot Air Fryer you will hear a faint sizzle as moisture kisses the hot metal and begins to evaporate, and a warm, toasty aroma emerges. Cook time creates a golden crust while keeping the interior tender, so spacing matters for even airflow. If they brown too quickly on top, reduce the temperature slightly or shorten the time, because overbrowning leads to a dry interior. A common error is stacking bagels or crowding the basket, which yields uneven cooking and soft spots where they touch.
Let the bagels cool slightly on a wire rack. Enjoy warm.: Cooling for a few minutes lets steam escape so the interior sets, preventing a gummy texture. The crust will firm up and the crumb will relax into a pleasant chew. Enjoying them warm highlights that contrast between crisp outside and tender inside. Resist cutting into them right away if you want neat slices, because rushing can compress the crumb. If you prefer a softer crust, cover them gently with a tea towel while they cool.