Marbled Chocolate Brioche Loaf

I love swirls of chocolate threading though any kind of a plain cake. This marbled brioche is fairly straightforward to prepare since you mix everything in the food processor. Marbling the plain and chocolate doughs together requires a little patience, but the reward is a beautiful loaf with an alluringly different flavor achieved by adding grated lemon zest and rum to the dough.

Makes one 9 x 5 x 3-inch loaf, about sixteen 1/2-inch slices

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BRIOCHE DOUGH

1/2 cup milk

2 1/2 teaspoons (1 envelope) active dry yeast

2 1/2 cups unbleached all-purpose flour (spoon flour into dry-measure cup and level off)

7 tablespoons cold unsalted butter, cold and cut into 12 pieces

1/4 cup sugar

1/2 teaspoon salt

1 large egg

2 large egg yolks

2 teaspoons finely grated lemon zest

1 tablespoon dark rum

CHOCOLATE ENRICHMENT

1 tablespoon water

1/2 teaspoon baking soda

Pinch of ground cinnamon

1 1/2 ounces bittersweet (not unsweetened) chocolate, melted and cooled

3 tablespoons unbleached all-purpose flour

One 9 x 5 x 3-inch loaf pan buttered and the bottom lined with a rectangle of parchment or buttered wax paper cut to fit

1. To make the brioche dough, heat the milk in a small saucepan until it is just lukewarm, about 110 degrees. Pour the milk into a small bowl and whisk in the yeast. Use a small rubber spatula to thoroughly stir in 1 cup of the flour thoroughly. Cover with plastic wrap and set aside for 20 minutes. The mixture will become bubbly and somewhat risen.
2. Combine the butter, sugar, salt, eggs, egg yolks, lemon zest, and rum in the bowl of a food processor fitted with the metal blade. Pulse repeatedly until the butter is evenly distributed throughout the resulting liquid. At this point the mixture may appear separated—it will come together as soon as some of the flour is added.
3. Scrape the yeast mixture into the bowl and pulse 6 times to mix it in thoroughly. Switch to the plastic dough blade and add the remaining flour and pulse again until the flour is completely incorporated and the mixture is smooth. Use a thin-bladed metal spatula to scrape down the inside of the bowl. Let the dough rest for 10 minutes.
4. Start the food processor and allow it to run continuously for 10 seconds. Invert the food processor bowl over a floured work surface to turn out the dough. Carefully remove the blade and transfer any dough on it to the surface. Use a bench scraper to fold the dough over on itself 5 to 6 times, adding pinches of flour if necessary, until it is slightly more elastic. Use a bench scraper or knife to divide the dough into 3 equal pieces.
5. Return one piece of the dough to the food processor. Cover the remaining pieces of dough with a dish towel or plastic wrap.
6. To prepare the Chocolate Enrichment, combine the water, baking soda, and cinnamon. Stir them into the melted and cooled chocolate. Scrape the chocolate mixture into the food processor bowl and pulse 3 to 4 times to incorporate. Add the flour and pulse continuously for 10 seconds, or until the dough is smooth. Invert the food processor bowl over a floured surface to turn out the dough. Carefully remove the blade and transfer any dough on it to the surface. Use a bench scraper to fold the chocolate dough over on itself 5 to 6 times, adding pinches of flour if necessary, until it is slightly more elastic.
7. Flour a cutting board and set it aside. Press one of the pieces of plain dough into a 5-inch square and place it on the cutting board. Repeat with the chocolate dough, arranging it directly on top of the square of plain dough on the cutting board. Repeat with the remaining piece of plain dough. The squares and the stacking don’t need to be perfect.
8. Use a knife or bench scraper to cut the stacked dough into 3 strips, each one about 1 3/4 inches wide. Then cut across one of the strips making ten 1/2-inch pieces. Slide the cut pieces of dough into a bowl. Repeat with the remaining strips of dough.
9. Slide your hands, palms upward, under the pieces of dough in the bowl and toss through gently a few times like a salad.
10. Sprinkle the pieces of dough in the bowl with 1 teaspoon of water to make them slightly sticky. Gently press and squeeze the dough together into a coherent ball. Invert the dough onto a floured work surface and press it into a thick 4 x 8-inch rectangle. Place the rectangle of dough in the prepared pan and gently press it to fill the pan completely.
11. Cover the pan with buttered plastic wrap and let the dough rise about 1 inch over the top of the pan, for 1 to 2 hours, depending on the temperature of the room.
12. About 20 minutes before the loaf is fully risen, set a rack in the middle of the oven and preheat to 350˚F.
13. Bake the loaf until it is well risen and deep golden, 35 to 40 minutes. Cool the loaf in the pan on a rack for 5 minutes, then unmold it and finish cooling it on its side to prevent it from compressing and becoming heavy.