Mix: Dissolve barley malt syrup in water in mixer bowl. Add bread flour, sugar, salt, and yeast. Knead on low until combined then medium until smooth, stiff, and passing the windowpane test.
First rest: Shape into a taut ball, cover, and rest 1 hour.
Divide: Degas and divide into 12 pieces of 135 g each. Roll into smooth tight balls pinching seams closed. Bench rest 10 minutes covered then 5 minutes uncovered.
Shape: Roll each ball into a log. Twist ends in opposite directions then bring together and roll seam firmly closed with palm of hand. Seal completely.
Float test: Place on a tray or dough container. Cover and rest at room temperature until bagels float when dropped in water. (around 30 min) Cold proof: Cover tightly and refrigerate overnight — 36 hours optimal, minimum overnight.
Preheat: Preheat oven to highest temp with baking stone or steel and lava rocks or cast iron for 45-60 minutes.
Boil: Bring a wide pot of water to a boil. Add barley malt syrup if using. Boil bagels 15-20 seconds per side. Drain on a wire rack. Add toppings immediately while surface is wet.
Transfer: Place on parchment paper and slide onto hot stone using a peel.
Steam and bake: Pour ¾ cup boiling water over lava rocks immediately. Bake 6 minutes with steam. Open door to release steam. Lower to 475°F and bake 10 more minutes until deeply golden and glossy.
Cool: Cool on wire rack 15-20 minutes before cutting.