Proof the yeast (if using active dry). In a small bowl, combine warm water and sugar, then sprinkle the yeast on top. Let it sit for 5–10 minutes until foamy. If using instant yeast, skip the proofing and add the yeast directly to the flour, but still warm the water.

Mix the dough. In a large bowl, whisk flour and salt. In a separate bowl, whisk eggs, yolk, and oil. Add the wet ingredients and yeast mixture to the flour. Stir with a spoon until a shaggy dough forms.

Knead until smooth. Turn the dough onto a lightly floured surface. Knead for 8–10 minutes, adding only enough flour to keep it from sticking. The dough should become smooth, stretchy, and slightly tacky but not wet.

First rise. Place the dough in a lightly oiled bowl, turning it once to coat. Cover with a clean towel or plastic wrap. Let it rise in a warm spot until doubled, about 1–1.5 hours.

Prepare for braiding. Gently deflate the dough and turn it out onto your work surface. For one large loaf, divide into 3 or 4 equal pieces. For two smaller loaves, divide the dough in half, then each half into 3 or 4 pieces.

Roll the strands. Roll each piece into a rope about 14–18 inches long, slightly thicker in the middle and tapered at the ends. If the dough shrinks back, rest it for 5 minutes and try again.

Braid. For a simple 3-strand braid, pinch the top ends together. Cross the right strand over the middle, then the left over the new middle, repeating down the length. Tuck the ends under. For a 4-strand braid, lay strands like parallel lines; weave the outermost right strand over–under–over to the left side, then repeat from the new right side until done. Keep the braid snug but not tight.

Second rise. Transfer the braid(s) to a parchment-lined baking sheet. Cover loosely and let rise until puffy and about 1.5 times bigger, 30–60 minutes depending on room temperature. The dough should slowly spring back when gently pressed.

Egg wash and top. Preheat oven to 350°F (175°C). Brush the braid generously with egg wash. Sprinkle sesame or poppy seeds if using. For extra shine, brush a second time after 10 minutes of baking.

Bake. Bake for 25–35 minutes for one large loaf, or 20–28 minutes for smaller loaves. The crust should be deep golden, and the internal temperature should reach about 190–195°F (88–90°C). If the top browns too fast, tent loosely with foil.

Cool. Let the challah cool on a rack for at least 45 minutes before slicing. This helps set the crumb and keeps it soft.