Tahini (or Peanut Butter!) Brioche

Directions

1. For the sponge, combine the milk, yeast, and sugar in the bowl of a stand mixer (you need a stand mixer). Whisk by hand to dissolve the yeast, then whisk in the eggs and stir in 1 cup of the flour. Sprinkle the remaining 1/3 cup over the top (don't stir it in). Cover and set aside to proof until there are cracks in the top layer of the dough and it's very soft to the touch, about 30 minutes.
2. To make the dough, add the flour, sugar, salt, eggs, egg yolk, and tahini or peanut butter to the bowl with the sponge. Use a dough hook to mix on low speed until the dough starts to come together. Scrape down the sides, then increase to medium speed and mix until you just see the dough come together around the dough hook, 8 to 10 minutes. It's important that the dough is developed before you incorporate the butter, so try not to rush the process.
3. Scrape the sides of the bowl, mix again on high speed, then add half the butter, working on medium speed. Once the first half of the butter is incorporated (you no longer see lumps)—this takes minutes, not seconds—add the second half. Continue mixing until the dough is silky smooth, 10 to 15 minutes (when I used peanut butter, this took closer to 20 minutes!). Increase the speed to medium-high and beat until the dough comes off the bowl, about 1 minutes. If you take a little piece of the dough and stretch it, you should see a gluten window, which indicates that the gluten is developed (when I was working with the peanut butter dough, I had to repeat the high-speed minute intervals a few times in order to achieve this elasticity; even then, it was still fragile/delicate).
4. Lightly flour a bowl or plastic storage container. Scrape the dough into the container and press it out in a flat rectangle. (Since the peanut butter dough was so soft, I used a generous amount of flour both in the bowl, on my hands, and on the dough's surface.) Fold the two sides in to meet in the middle, then flip over and press it out, back into a flat-ish rectangle. Cover and refrigerate for 6 hours, or up to overnight. After refrigerating, you can shape the dough. You can wrap the shaped loaves and freeze them for up to 5 days.
5. To make the loaves, lightly flour a work surface and butter two 9-inch loaf pans. Divide the dough in half, then roll one half into a 2- by 6-inch rectangle, divide into three long strips, braid together, and tuck into the loaf pan. Repeat with the second piece of dough. (You can also make the second piece of dough into balls, then pile those into the loaf pan.) Alternatively, this is a place where you can go wild! Spread jam over the dough then roll it into a log and either tuck that whole roll-up into the pan, or slice into cinnamon bun-like swirls and tuck them in haphazardly (or in an organized fashion).
6. To make rolls, butter a 9-inch springform. Then divide the dough into 12 pieces and use a cupped hand to gently roll each one in small circular motions against the surface to form a tight ball. Arrange them in the pan in a single layer, with 8 around the circumference and 4 in the center.
7. Cover whatever you've shaped loosely with plastic wrap and let rise until doubled in size (2 to 2 1/2 hours for the loaves; 1 1/2 to 2 hours for the rolls). To test to see if they've proofed properly, press down on the dough with your finger: It should feel pillowy-soft and spring back almost all the way, still leaving a small indentation.
8. Heat the oven to 350° F. Make an egg wash by whisking together the eggs and the milk. Brush the dough with egg wash and sprinkle sesame seeds over top, if using (flaky salt is also a good addition here). Set on a baking sheet and bake until golden brown, 40 to 45 minutes for the loaves, 15 to 20 minutes for the rolls.
9. Let the loaves cool in their pans on a wire rack. For the rolls, snap off the outside of the springform pan, then let cool on the pan bottom on a wire rack.