In the bowl of a stand mixer fitted with the dough hook, combine the flour, 550 grams of water, yeast, salt, sugar, and oil. Mix on low to bring the dough together, then knead on medium speed for 10 to 15 minutes, until smooth and elastic. If the dough looks stiff or dry, add up to 30 grams more water, 1 tablespoon at a time. You can also knead the dough by hand on a lightly floured surface.

Shape the dough into a smooth ball, lightly coat with oil, and transfer to a large bowl. Cover tightly with plastic wrap and let rise in a warm place until doubled, 1 to 1½ hours. (For a deeper flavor, refrigerate the dough overnight after the first rise.)

Turn the risen dough onto a work surface and divide into 12 to 14 portions of 160 grams each. Cover loosely with plastic wrap and let rest for 30 minutes. If the dough feels sticky, spray lightly with oil.

Roll each piece into a medium-length rope, gently tightening the strand. Cover and let rest for another 30 minutes.

Braid the dough as desired (a 4-strand braid is recommended) and place each loaf in a 9x4-inch/23x10 cm loaf pan. Cover loosely and let rise until puffy and jiggly when nudged, 45 to 60 minutes.

Heat the oven to 390°F (200°C), using static heat. Brush the tops of the loaves with beaten egg and sprinkle with coarse salt. Place pans on the lowest oven rack and bake for 22 to 26 minutes, rotating if needed. Start checking at 18 minutes; the loaves should be deeply golden.

Let the challah loaves cool in the pans for 10 minutes, then transfer to a wire rack. Slice once just warm, or let cool completely.