Make the sponge:
Pour the yeast into the bowl of a standing mixer. Heat the milk in a small saucepan over low heat to a temperature that is warm to the touch, about 100°F, and pour it over the yeast. Stir together with a spoon to combine. Add the honey, Kamut flour, and millet flour and stir again. Add the all-purpose flour to the top of the sticky dough, then the salt. Do not stir. Let the sponge sit for approximately 30 minutes, until the flour begins to crack and the sponge seeps upward.
Make the dough:
While the sponge sits, set the eggs, in their shells, into a bowl of hot water to bring them to room temperature.
After 30 minutes, crack the eggs and add them to the sponge. Put the bowl onto the mixer with the hook attachment and mix on low until the flour is incorporated, scraping down the sides of the bowl with a spatula.
Watch the dough to see if it’s sticking to the sides. If it is, add additional allpurpose flour, 1 Tbs. at a time—it may take as much as 1/2 cup until the dough is pulling away from the sides of the bowl. Once the dough has formed a cohesive mass and is pulling away from the sides, turn the mixer to medium and set a 5-minute timer. The dough will be moister than many bread doughs and will mostly cohere around the hook, occasionally letting off a tail of dough. Listen for the slapping noises as the dough goes around and around, releasing and incorporating the tail of dough. Halfway through the mixing time, stop the mixer and scrape the dough thoroughly from the hook. Mix the dough for 5 minutes more, making sure to set a timer.
After 10 minutes the dough should be a supple, elastic mass. Add the butter 1 Tbs. at a time and mix on medium speed, waiting to add the next piece until the first one is fully incorporated. The dough will come apart and back together again as the butter is incorporated into the dough. Once all the butter is added, the dough should be shiny and soft.
For the first rise, scrape the dough into a buttered bowl, cover with a towel or plastic wrap, and leave to rise for 2 hours, or until doubled in size. The dough is ready when a floured finger stuck into it leaves an impression. Scrape the dough onto a lightly floured work surface and gently fold the dough into itself and gather it back into a ball. Cover the bowl with a towel or plastic wrap and chill overnight.
Finish the babka:
Preheat the oven to 350°F. Rub a 10-inch tube or Bundt pan with butter, then lightly dust it with sugar. Toast the pecans in the pan until golden, about 15 minutes. In a small bowl, stir together the brown sugar, granulated sugar, and salt.
Dust a work surface with flour. Remove the challah dough from the refrigerator, flour the top, and scrape the dough onto the work surface. Dust the top of the dough with flour and roll into a rectangle about 10 inches by 16 inches.
Rub the softened butter evenly over the surface of the dough. Sprinkle the sugar mix over the butter, then break up the pecans a bit and sprinkle them on top of the sugar. Sprinkle the chocolate last. Starting at the 16-inch length, roll the dough into a tight log. Cut the log into 13 pieces, each about 1-1/4 inches thick.
Place the pieces in the pan in a haphazard way, so that as the dough proofs the odd-shaped spaces are filled in. Here is one way: Create the bottom layer by laying 4 circles at the bottom of the pan with the spirals facing up. Set a circle upright in between each of those circles. For the top layer, set 3 circles in areas that will create empty pockets. Slice the last 2 circles in half and fit them into the gaps that remain. Cover the pan with a towel and let the dough rise until doubled in size, about 2 hours.
Bake for 45 to 50 minutes. The babka should be a beautiful golden-brown on top and have risen to the top or slightly over the top of the pan. Let it cool slightly, about 15 minutes, before placing a rack on top of the pan and turning the pan upside down to get the babka out of its pan and onto the rack to cool.
Make Ahead Tips
The babka is best eaten the day it’s made. It can be stored, wrapped tightly in plastic, for up to 2 days. When you eat the babka after it’s been stored, warm it first.
Photo: Quentin Bacon