Remove the bagels from the refrigerator, and let rest 1 to 2 hours. The bagels should rise a bit.
After the bagels have rested for about 60 to 90 minutes , preheat oven to 450ºF / 230 ºC. This will allow the oven to come up to temperature while the bagels are rising.
As the oven is warming, fill large pot with water and bring to a boil on the stove.
When the bagels are finished rising and the oven is preheated, add the baking soda (if you're using it) to the boiling water.
Now gently place 3 or 4 bagels into the boiling water. (You will cook the bagels in 2-3 batches.) Wait 40 seconds, flip the bagels, and boil them for another 40 seconds.
Using a slotted spoon, remove the bagels from the water and let them drain on a cooling rack. Let cool for 10 minutes or so, and repeat the boiling process with the remaining batch(es).
While bagels are cooling, combine the white of one egg with 1 tablespoon of water
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 to 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.