In the bowl of a stand mixer, add: sourdough starter, water, brown sugar, vanilla extract, ground cinnamon, bread flour, salt. Use the dough hook attachment to knead on medium-high speed until combined. Then add the butter. Continue kneading for 5-7 minutes or until the dough becomes smooth and elastic.

No mixer? Mix everything together in a large bowl, then knead by hand on a clean surface for 7–10 minutes.

Lightly grease a medium bowl with oil or butter and place the dough inside. Cover with greased plastic wrap or a damp towel. Let rise at room temperature for 3–6 hours, or until the dough has risen by at least 50% and looks slightly puffy.

Transfer the covered dough to the refrigerator and let it ferment for 8–24 hours.

Line a baking sheet with parchment paper. Then cut 8 squares of parchment paper for each bagel to rest on during their second rise.

Remove dough from the fridge. Divide into 8 equal portions (about 120 g each) for large, bakery-style bagels. Roll each piece into a tight ball. Allow the dough balls to rest for 15 minutes before shaping.

Poke a hole through the center using your thumb. Gently stretch into a ring about 1½–2 inches wide.

Place shaped bagels on their parchment squares. Cover the bagels loosely with greased plastic wrap. Let rise for 1-2 hours, or until puffy and visibly risen.

Preheat your oven to 220°C (425°F). In a large pot, combine the water and brown sugar. Bring to a gentle boil over medium-high heat.

Carefully lower bagels into the boiling water. Boil each bagel for 30-40 seconds per side. Work in batches of 2–3 bagels at a time.

Place boiled bagels back onto the parchment-lined baking sheet.

In a small bowl, mix together the brown sugar, granulated sugar, flour, and cinnamon. Stir in melted butter until the mixture forms a crumbly, slightly clumpy texture.

Brush each bagel generously with the whisked egg. Spoon and gently press the cinnamon crunch topping onto each bagel so it sticks well.

Bake at 425°F (220°C) for 20-25 minutes, or until they are golden brown, the topping is crisp, and the internal temperature is 200℉-210℉ (93.3℃-98.9℃).

Allow bagels to cool on a wire rack for at least 15–20 minutes before serving.