Prunes mixed into the dough in place of raisins offer a deeper, more caramel flavor while dried plum powder helps heighten the flavor of the cinnamon. For the best results, make the sponge the day before.
Yield: Two [22-by-11-cm / 8-by-4-inch] loaves
340 g / 2 1/2 cups all-purpose flour
15 g / 1/3 cup unprocessed wheat bran
405 g / 1 3/4 cup water
4 g / 1 teaspoon active dry yeast
310 g / 2 1/4 cups all-purpose flour
3 g / 1 teaspoon active dry yeast
130 g / 9 tablespoons unsalted butter, at room temperature
12 g / 1 heaping tablespoon kosher salt
55 g / 1/4 cup sugar
5 g / 1 tablespoon cinnamon
4 g / 1 tablespoon Dried Plum Powder
4 g / 1 tablespoon orange zest
50 g / 1 each egg, beaten with a splash of water
Make the sponge: In a bowl, whisk together the flour, water, wheat bran, and yeast and let sit at room temperature for 30 minutes. Refrigerate overnight. Bring to room temperature 1 hour before proceeding to the next step.
Make the dough: Mix the flour, bran, and yeast into the sponge until a shaggy dough forms. In a stand mixer fitted with a paddle attachment, briefly mix the butter. Add the sponge-flour mixture to the butter and mix on low speed until the butter is no longer sticking to the sides of the bowl. Let the dough rest for 20 minutes.
Attach the dough hook to the mixer. Add the salt and mix on medium speed until the butter is thoroughly incorporated and the dough pulls cleanly away from the sides of the bowl, 5 to 7 minutes. Add the prune bits or dried plums and mix on low speed until evenly distributed in the dough.
Put the dough in a lightly oiled bowl, cover, and let rise until doubled in volume, about 1 1/2 hours. Place the dough on a lightly floured surface and pat into a rectangle. Fold in 3 folds like a business letter. Return the dough to the bowl, cover, and refrigerate for 1 hour.
Make the filling: In a small bowl, mix together the sugar, dried plum powder, cinnamon, and orange zest.
Put the dough on a lightly floured surface and cut it in half. Roll each half into an 18 x 35.5 cm [7 x14-in] rectangle. Brush the surface with egg wash, leaving a 1.25-cm [.5-in.] border. Sprinkle with half of the cinnamon filling. Starting with the short end of the rectangle, roll the dough into a log. Using the palms of your hands, gently roll the log to eliminate air pockets between the swirl layers. Repeat with the remaining dough and filling.
Oil two 21.5 x 11.4-cm [8.5 x 4.5-in.] loaf pans. Tuck in the ends of the dough log and place, seam-side down, into the lightly oiled loaf pan. Loosely cover the loaf pans and let the dough rise until it no longer springs up when pressed with your fingertips, about 1 1/2 hours.
Preheat the oven to 350F [180C]. Bake the loaves, rotating once, until the tops and edges are golden brown, about 50 minutes. Cool in the pans for 5 minutes, then unmold and cool completely.