Combine wet: To the bowl of a stand mixer, add the sourdough starter, warm water, and sugar. Mix until smooth and milky in appearance.
Add dry ingredients: Add the einkorn flour and salt. Using the dough hook attachment, mix on stir setting or low speed until the flour is fully absorbed and the dough begins to pull away from the sides of the bowl, about 1–3 minutes.
Bulk ferment: Remove the dough and gently shape into a ball and place it back into the cleaned bowl. Cover with plastic wrap and let ferment for 3–6 hours, or until nearly doubled and slightly airy with small bubbles throughout.
Cut parchment squares: Cut parchment into 8 individual squares, slightly larger than a bagel and place them on a large baking sheet.
Shape the dough: Gently transfer the dough to a clean work surface. Divide into 8 equal portions (about 95-100g each). Carefully shape each piece into a ball without deflating the dough. I like to gather the sides, pinching them in the middle, then turn seam-side down and gently roll using a “C” motion with your hand to create light surface tension. Poke a hole through the center with your finger, then gently stretch the hole to form a bagel shape.
Cover and proof: Place the shaped bagels on a parchment-lined baking sheet, then cover with a damp tea towel. Let them proof in a warm area of your house (an oven with the light on works great) for about 1.5–2 hours. You’re looking for a slight puffiness, this will be more subtle than with regular bread flour.
Preheat oven: Preheat oven to 425 degrees Fahrenheit
Prepare the water bath: Bring 6 cups of water, the sugar, and baking soda to a boil in a large pot.
Boil the bagels: Working with 2–3 bagels at a time, carefully lower each bagel into the boiling water with the parchment square still underneath. After about 10–15 seconds, the parchment will release from the bagel. Carefully remove the parchment with tongs and place it back on the baking sheet to reuse for baking. Continue boiling the bagels for 10–15 seconds per side, then transfer them back onto their original parchment squares. Repeat with the remaining bagels, reusing each parchment square.
Add toppings: Immediately sprinkle the boiled bagels with your desired toppings, such as everything bagel seasoning, sesame seeds, or cheese. The surface will be tacky right after boiling, which helps the toppings stick.
Bake: Bake for 13–15 minutes, or until golden brown and the internal temperature reaches 200–210°F.