based on the La Brea Bakery sourdough book, which I highly recommend
1.5 c cool water
1.5 c sourdough starter
1 packet active dry yeast
2 egg yolks (or zero for plain bagels, or I'd add more next time for eggier bagels)
1/4 c = 4 T sugar
2 T barley malt syrup
6 T nonfat milk powder
1 T salt
~6 c white bread flour + 6 t vital wheat gluten (or use high-gluten flour if you have it)
Kitchenaid, semolina flour, parchment paper, baking sheets, pot for boiling water
Get out the Kitchenaid and put on the dough hook. Dump all the wet ingredients plus 4 c gluten-enriched flour into the bowl and mix on low to combine, slowly adding the rest of the flour. When the dough looks combined, turn up the speed to medium and mix for several minutes or until the dough is pretty much climbing out of the bowl.
When the Kitchenaid can do no more, turn the dough out onto a clean *not floured* surface and knead firmly for several more minutes. By the time you're done kneading, the dough should be firm, smooth, and supple, and will begin to feel slightly moist on the surface. You want as much gluten development as you can get, so the more kneading the better. Roll the dough into a smooth sphere, cover with a cloth, and let sit on the board for 10 min. Cut into 18 equal-sized pieces, roll each into a little ball, cover with the cloth again, and let sit for 15 min.
Prepare two baking sheets by lining with parchment and sprinkling the parchment with semolina. With each little ball of dough, roll it on the unfloured board into a rope of uniform thickness, about the length of the spread of your hand (thumb-tip to pinky-tip) or a bit longer. Gently hold one end between your thumb and the base of your pointer finger, and loop the rest around the back of your hand and onto your palm; the two ends should overlap by an inch or two on your palm. With the dough looped around your hand, seal the ends together by lightly rolling them between your palm and the board until the whole bagel is of uniform thickness. Take the bagel off your hand and place it on the prepared baking sheets, keeping at least an inch between bagels. Cover each baking sheet with a cloth and put in the fridge overnight.
In the morning, take out of the fridge and let warm up a bit. Start preheating the oven at 450F and start boiling several inches of water in a large pot. When the water is fully boiling, gently remove three bagels from the sheets and drop them into the water. They should float; mine didn't, which means they were too cold and/or not risen enough, but maybe it's just fine because they turned out beautifully. If floating, hold them under the surface for 10 seconds, then let float for 10 seconds; if sinking, detach from the bottom after a couple seconds, then let boil for about 20 seconds. Sprinkle more semolina on the parchment while the bagels are boiling. Lift each bagel out of the water with a slotted implement and place onto a re-semolina-ed spot on the parchment. Let the water return to a boil and repeat with the rest of the bagels. Turn the oven down to 400F and bake for 20-25 min until golden brown, rotating the sheets half-way through and moving up or down in the oven to control the browning on the bottom. (You can roast an eggplant for this at the same time!) Transfer to cooling racks, eat when warm or room temperature, and store the rest in a plastic bag.