Bring a large pot (about 9-by-4-inches high) of water to a boil. Stir in the molasses or sugar and baking soda until dissolved. With a skimmer, transfer the bagels, one at a time, to the boiling water, without crowding them; cook them in batches of 2 to 3 at a time so that they can swim around without touching one another. If they are slightly underrisen, they may sink at first but will then rise to the surface. Boil for 30 seconds to 2 minutes on each side, gently flipping them over with the skimmer; the longer time will make a thicker crust. Remove the boiled bagels, shaking off excess water over the pot and set onto parchment or the unfloured towel to drain, then move them, using a pancake turner, to the prepared baking sheet(s) or peel, after just 30 seconds to 1 minute, so that they don’t stick. The bagels will look wrinkled at this stage. Don’t worry — their appearance vastly improves on baking.