For the Dough:
1½ cups water
3 tablespoons fresh yeast
6 cups sifted all-purpose flour
6 tablespoons sugar
1 tablespoon salt
¼ cup melted butter
For the Topping:
1 egg, beaten
Sesame and poppy seeds
1. Make the dough: Place the water in a stand mixer outfitted with a dough hook and crumble the yeast on top. Add the flour, eggs, sugar, salt and butter, in that order, and mix on low speed for 5 minutes until combined.
2. Transfer the dough to a floured work surface and knead until the dough is smooth, another 5 minutes. Place the dough in a large floured bowl and cover with a towel. Set in a warm area to rise until doubled in size, about 40 minutes.
3. Uncover the dough and divide into 3 equal portions. Divide each third into 3 equal parts and roll each into a 10-inch long rope.
4. To braid the dough, align 3 dough stands vertically in front of you on a parchment-lined baking sheet, about 2 inches apart. Pinch the furthest ends together and begin braiding the ropes until you reach the opposite end. Repeat with the remaining dough. Cover the loaves with a kitchen towel and allow to rise until doubled in size, about 30 minutes.
5. Preheat the oven to 425°. Brush the challah loaves with the beaten egg. Sprinkle them generously with sesame and poppy seeds and bake until the loaves are golden brown, about 25 minutes. Remove from the oven and let the loaves cool on a rack before serving.