Rainbow Friendship Challah Bread
Whisk yeast, 2 teaspoons sugar, and ¼ cup warm water in the bowl of a stand mixer. Let sit until foamy, about 10 minutes.
Whisk eggs, salt, ½ cup butter, ¾ cup sugar, and 2 cups warm water in a medium bowl. Add eggs and 7 cups flour to yeast mixture. Beat with dough hook on medium speed until dough is smooth, elastic, and very sticky and pulls away from sides of bowl, about 10 minutes.
Grease a large bowl with butter and transfer dough to bowl. Cover with plastic wrap and let sit in a warm place until doubled in size, about 2 hours.
Turn out dough onto a lightly floured surface and divide into 6 equal portions. Roll each out into a long rope, about 12 inches long. If you want a rainbow loaf, dye each dough rope a different color by working drops of food coloring into each rope.
Grease a baking sheet with butter. Place the 6 ropes side by side on the sheet. Working with one at a time, pinch logs together at 1 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 egg yolks and 2 tablespoons water in a small bowl. Brush dough with egg wash. Bake loaf for 15 minutes, then increase oven temperature to 425 and continue baking until browned and sounds hollow when tapped, 15–20 minutes more. Let cool on baking sheet.
Adapted by Bon Appetite