Combine the active sourdough starter, water, and flour in a bowl. Mix until fully integrated, then cover and allow it to rest in a warm place for about four hours, or until the levain has doubled in volume.

In the bowl of a stand mixer fitted with a dough hook, mix together the flour, water, and levain. Let the mixer run for approximately 2 minutes until a rough dough forms. Cover the bowl and let it rest for 30 minutes (autolyse).

After the resting period, restart the mixer and add the salt, barley malt syrup, and olive oil. Knead on medium speed for 10 minutes. By this time, the dough should be elastic, strong, and non-sticky.

Lightly oil a large bowl with olive oil and transfer the dough into it. Cover and let it rise for four hours at around 75°F (24°C).

Place the dough in the refrigerator for a cold-proof period of 10-15 hours.

Turn the dough out onto a lightly floured surface and divide it into ten equal parts. Use a kitchen scale for precision. Shape each portion into a tight, seamless round. Poke a hole in the center of each round with your finger and stretch the hole to about 1.5 inches (3.5 cm) in diameter.

Line two baking sheets with parchment paper and dust them with rice flour or semolina. Arrange the shaped bagels on the trays.

Proof the bagels for 1.5 to 3 hours at approximately 75°F (24°C) until they have slightly risen and appear puffed and relaxed.

Preheat your oven to 430°F (220°C) about 30 minutes before baking. Simultaneously, bring a large pot of water to a rolling boil.

Add the sugar and baking soda to the boiling water. Boil the bagels, 3-4 at a time, for 1 minute on each side. Transfer the boiled bagels to a clean kitchen towel to drain before placing them on a lined baking tray.

Generously brush each bagel with olive oil and sprinkle za'atar seasoning on top. Bake in the preheated oven for 15-20 minutes until they achieve a golden brown color. Move the baked bagels to a wire rack and let them cool for at least 15 minutes before serving.