Remove the bagels from the refrigerator, and let rest 20 minutes
While the bagels are resting, preheat oven to 450ºF / 230 ºC
Fill large pot with water and bring to a boil on the stove
Make the egg wash for the bagels by combining the white of one egg with 1 tablespoon of water (see NOTE below for vegan version)
Once the water boils (and the bagels have been out of the fridge for at least 20 minutes), add the baking soda to the boiling water.
Gently place 3 or 4 bagels into the boiling water. (You will cook the bagels in 2-3 batches.) Wait 30 seconds, flip the bagels, and boil them for another 30 seconds.
Using a slotted spoon, remove the bagels from the water and let them drain on a cooling rack. Repeat the boiling process with the remaining batch(es).
After bagels have cooled, brush each gently with the egg wash. If topping the bagels (e.g., with sesame seeds), now is the time to do it. (The egg wash will help make the topping stick to the bagels.)
Gently place the bagels on a clean rimmed baking sheet lined with parchment paper. Slide the rimmed baking sheet into the hot oven, and cook until golden brown, about 16-18 minutes. Be sure to rotate the pan halfway through the bake.
When bagels are done, remove them from the oven and let them cool on a rack. Eat warm or at room temperature.
NOTE: For a vegan version, substitute a mix of 2T of plant-based milk and 2 tsp of maple syrup for the egg wash.