Combine the yeast, sugar, and 1/2 cup water in the bowl of a stand mixer. Let sit for 5-10 minutes, or until the yeast starts to foam or "bloom". If the yeast does not bloom, you may need to get fresher yeast.
Add the remaining water, eggs, egg yolks, honey, and butter, mixing to combine. Place the mixing paddle with the dough hook.
Add the flour and salt, one cup at a time, mixing on low using the dough hook. Knead until soft, and tacky, but not sticky, adding more flour, as needed.
Transfer to a clean, oiled bowl. Cover with a damp towel or plastic wrap, and let rise in a warm place until doubled, about 1 hour.
Meanwhile, preheat the oven to 350°F. Line a baking tray with parchment paper.
Punch down the dough to remove and air bubbles, and transfer to a floured surface.
Cut the dough into 6 even pieces, roll each piece into a rope approximately 12 inches long. Cover with a damp cloth and let rest for 10-15 minutes.
Braid the challah according to your preference.
Make the egg wash: whisk together the egg and water, brush overtop the braided challah and sprinkle with seeds, if using.
Bake for 40-45 minutes, turning the tray halfway through, and brushing with additional egg wash.
Enjoy!
