2 tablespoons dried onion, rehydrated with 2 tablespoons water
For Boiling and Baking
1 tablespoon baking soda
1 to 2 teaspoons malt syrup
For the sponge: In the bowl of an electric mixer, combine the bread flour, yeast, and water. Mix well with a wooden spoon until a smooth, sticky, batter forms. Scrape down the sides of the bowl. Cover and set aside at room temperature until light and bubbly and practically doubled in size, 2 to 3 hours.
For the dough: To the bowl with the sponge, add the yeast, 3 cups of the bread flour, the salt, and malt syrup. Using the hook attachment, mix on low speed until a rough dough is formed. Add more flour as needed to form a ball. Mix on medium-low speed to knead the dough until pliable and smooth, about 6 minutes. If the dough feels too tacky add a touch more flour. If it feels too dry add water 1 teaspoon at a time. The dough should be able to be stretched thin enough to allow light through without tearing.
Divide the dough into 4-ounce pieces and form them into smooth balls, tucking the edges underneath. Cover the balls with a damp towel and allow them to rest for 10 minutes.
Line 2 baking sheets with parchment paper and lightly brush the paper with olive oil. Form a bagel out of each ball by poking a hole in the center of a dough ball and working your thumb around the inside of the hole until you have a ring. Place the rings on the prepared baking sheet and cover them again with the damp towel. Allow to proof for another 20 minutes.
To test the bagels, fill a bowl with water and place one bagel in the bowl. The bagel should float to the surface. If it doesn’t, allow the bagels to proof for another 10 minutes. Place the baking sheets in large bags or cover with plastic wrap and place in the refrigerator to slowly proof, overnight or up to 2 days.
For the topping: In a small bowl combine the white sesame seeds, black sesame seeds, flaxseed, hemp seeds, poppy seeds, fennel seeds, caraway seeds, salt, and rehydrated onion. Set aside.
When ready to bake, preheat the oven to 500℉. Position the racks on the upper third and lower third of the oven.
For boiling and baking: Fill a large shallow saucepan with water and bring to a boil over high heat. Add the baking soda and malt syrup to the water.
Gently drop as many bagels as will fit comfortably into the boiling water. They should float to the surface. Cook for 2 minutes on the first side before flipping them gently with a slotted spoon and cooking for another 2 minutes on the second side. Use a slotted spoon to remove the bagels from the water, tapping to remove as much excess water as possible. Place the bagels, smooth-side down directly into the bowl with the seed mixture. Transfer them to the baking sheets, topping-side up. Sprinkle with additional topping if needed. Continue with the remaining bagels.
Bake the bagels for 5 minutes. Rotate the baking sheets top rack to bottom rack and turn them 180 degrees. Reduce the temperature to 450℉ degrees. Continue to bake until they are lightly golden brown and sound hollow when tapped on the bottom, another 5 to 6 minutes.
Allow the bagels to cool for at least 15 minutes before tearing into them.