Whisk yeast into flour. Add water and stir until it forms a thick, sticky batter (like a pancake batter). Cover the bowl with plastic wrap and let stand at room temperature until very foamy, about 2 hours. When the bowl is tapped on the counter, the foam should collapse. Transfer sponge to mixing bowl of stand mixer. Add yeast, 3 cups of flour, egg yolks, salt and malt (or equivalent). Mix on low with dough hook until combined and a ball forms. Slowly add remaining flour to form a stiff dough. Turn machine up to medium-high and knead for six minutes (or hand-knead for 10 minutes). The dough should be stiff, but pliable and satiny, not sticky. If too dry, add water in 1/4-1/2 tsp increments; if too tacky or sticky, add more flour in small increments. A small piece of dough should be able to stretch enough to shine light through without tearing (windowpane test). Divide the dough into 12 pieces, 4.5 ounces each, for standard bagels, or smaller if desired. Form into neat rolls and cover with a damp towel. Allow to rest at room temperature 20 minutes. Line 2 sheet pans with parchment (or Silpats) and spray lightly with oil spray. Form bagels - you can poke a hole with your thumb, then evenly stretch the dough until the hole is about 2 1/2 inches across (be sure the rim of dough remains evenly thick); or you can form the dough into an 8-inch rope, then overlap the ends and seal them together by rolling them firmly under your palm against the countertop. Form into neat circles on the lined baking sheets, spray lightly with oil and cover loosely with plastic wrap. Let stand at room temperature for 20 minutes. Fill a deep bowl with cool (not cold) water. Place one bagel in the water; if it does not float in the first 10 seconds, dry it off, put it back on the tray and wait 10 minutes, then repeat. If it does float within 10 seconds, dry it off, return it to the tray, replace the plastic wrap cover and place both trays in the refrigerator overnight (or up to 48 hours). Preheat the oven to 500°F Set two racks in the middle of the oven. Bring a large, wide pot of water to a boil and add the baking soda. Remove bagels from refrigerator and add to boiling water a few at a time - don't crowd them. They should float within 10 seconds. Boil on one side for 60 seconds, then flip and boil on the other side for 60 seconds. (If you like a very chewy bagel, you can increase that to 2 minutes per side). While the bagels boil, sprinkle the baking sheet with cornmeal or semolina. (If you decide to place fresh parchment, be sure to spray it with oil spray first.) Remove the bagels from the water with a slotted spoon, skimmer or spider and place on the prepared baking sheets. If using optional poppy seeds, dip one side of the bagel in the seeds as you remove them from the water, then bake seed-side-up. Place the pans in the preheated oven, one on each shelf. After 5 minutes, rotate each pan 180° and switch racks (if baking one at a time, keep it on the center rack, but still spin it around). Lower the oven to 450F and bake another 5-6 minutes, until the desired color is achieved (egg bagels are traditionally baked to a light golden brown, but you may bake them darker if you like). Let cool on a rack at least 15 minutes before serving.