Challah

Whisk 2 (¼-oz.) envelopes active dry yeast (about 4½ tsp.), 2 tsp. sugar, and ¼ cup warm water in the bowl of a stand mixer fitted with a dough hook (or a large bowl if kneading by hand). Let sit until foamy, about 10 minutes.

Whisk 2 large eggs to blend in a medium bowl. Add 2 cups (16 oz.) warm water, 4¾ tsp. Diamond Crystal or 2½ tsp. Morton kosher salt, ½ cup shortening, melted, and remaining ¾ cup sugar and whisk to combine.

Add egg mixture and 7 cups (875 g) all-purpose flour to yeast mixture. Beat on medium speed until dough is smooth, elastic, and very sticky and pulls away from sides of bowl, about 10 minutes. (Alternatively, knead dough on a lightly floured work surface until smooth and elastic, about 10 minutes.)

Grease a large bowl with shortening; transfer dough to bowl. Cover with plastic wrap and let dough rise in a warm place for 1½–2 hours (or chill for 8–12 hours), until doubled in size.

Turn dough onto a lightly floured surface and divide into 6 equal portions. Shape each into a 17"-long rope. Grease 2 rimmed baking sheets with shortening. Place 3 ropes side by side on each prepared sheet. Working with one at a time, pinch ropes together at one end; braid, then pinch ends together and tuck under. Let sit in a warm place until 1½ times larger, about 1 hour.

Preheat oven to 325°. Beat 2 egg yolks and 2 Tbsp. water in a small bowl. Working with one at a time, brush braided bread dough with egg wash and sprinkle with sesame seeds or poppy seeds (if using). Bake first loaf 15 minutes, then increase oven temperature to 400° and continue baking until browned and challah sounds hollow when tapped, 15–20 minutes more (an instant-read thermometer inserted into the center of the loaf should read 200–210°). Let cool on baking sheet.

Reduce oven temperature to 325°, then leave oven door open 5 seconds to cool down. Repeat baking with remaining dough. Do ahead: Challah can be made 3 days ahead; keep tightly wrapped at room temperature, or freeze up to 1 month. Let cool before storing.