Make the light dough
In the bowl of a stand mixer fitted with the paddle attachment, mix the flours, salt, yeast, caraway seeds (if using), water, oil, and molasses on low speed until combined, about 1 minute. Increase the speed to medium low and mix until well combined and the sides of the bowl are clean, about 1 minute more. Switch to the dough hook and knead on medium-low speed until the dough is smooth and tacky (it should peel off your finger when you poke it, like a Post-it note), about 4 minutes. If the dough is too sticky, add more bread flour 1 Tbs. at a time, kneading to incorporate. If it’s very stiff, knead in water 1 Tbs. at a time. (Alternatively, you can mix the dough in a large bowl by hand and then knead on an oiled surface; mixing and kneading will take longer.)
Rub a little vegetable oil on a work surface to create an 8-inch circle, and put the dough on this spot. Using your hands, stretch and fold the dough up and over itself from all four sides into the center, crimping it where the folded ends meet, to form it into a tight, round ball that is smooth on the bottom.
Invert the dough ball, setting it seam side down in a lightly oiled bowl that’s twice the size of the dough. Tightly cover with plastic wrap. Let sit at room temperature until doubled in size, about 1-1/2 hours.
Make the dark dough
Immediately after making the light dough, repeat the process to make the dark dough, adding more water if needed to make a dough with the same feel as the first dough. Stretch and fold the dough into a ball and let it rise in another lightly oiled bowl as described above.
Shape the loaves
Author's note: Making the swirl is as easy as stacking alternating layers of light and dark dough and then rolling the stack into a loaf shape. Start by forming the dough layers into squares, which will roll up into an even loaf (unlike circles, which can yield a tapered loaf). I use a light coating of oil on my work surface instead of flour because it keeps the dough supple and easy to work with, and there’s no risk of incorporating too much flour, which would dry out the dough.
When both doughs have doubled in size, divide each into 4 equal pieces (about 5 oz. each). Generously coat the inside of two 8-1/2 x 4-1/2-inch loaf pans with cooking spray.
Rub a little vegetable oil on a work surface, move two pieces of each dough to the oiled area, and flatten them with the palm of your hand. Using your hands or a rolling pin, gently shape each piece into a 6-inch square that’s about 1/4 inch thick.
Make a stack of the dough squares, starting with a light dough square on the bottom, then a dark square, then a light, and then the final dark piece; the bottom light piece will become the outside of the loaf. Firmly pat down the stack with the palm of your hand or lightly roll it with the pin so that all four pieces adhere to one another.
Starting with the side closest to you, tightly roll the stack up into a loaf, pinching the seam closed with your fingertips to seal, if necessary. Repeat with the remaining dough for the second loaf.
Set each loaf seam side down. Gently roll and stretch each until it’s the same length as the pans. Place each loaf of dough seam side down in the pans, coat the tops with cooking spray, and cover the pans loosely with plastic wrap.
Let the loaves rise
Author's note: A second rise further develops the dough’s flavor and relaxes the gluten strands inside, while also letting the dough rise to its proper size and shape before baking. If your kitchen is on the warm side, the loaves will rise faster, and vice versa.
Set the loaves aside at room temperature until nearly doubled in size with tops that are about an inch above the edges of the pans, 1 to 2 hours. At this point, pressing on the dough with your finger should make a dimple that springs back slowly. If it springs back quickly, give the dough another 15 to 30 minutes to rise.
Bake the loaves
Author's note: Baking is the ultimate transformation: Dough goes into the oven, and bread comes out. A light coating of egg wash—a mixture of beaten egg and water—gives the crust color and shine after baking. Underbaking yields gummy bread, so use an instant-read thermometer to check for doneness; inserting it close to the edge of the pan (without touching the pan) leaves a less noticeable hole.
Position a rack in the center of the oven and heat the oven to 350°F.
In a small bowl, whisk the egg with 1 Tbs. water and then lightly brush the tops of the loaves with the egg wash; discard any remaining egg wash. Bake for 20 minutes, then rotate and swap the positions of the pans. Continue baking until the loaves are a rich golden brown and an instant-read thermometer inserted into the center registers 190°F to 195°F , 20 to 25 minutes more. Transfer the loaves in their pans to a wire rack to cool. When cool enough to handle, remove the bread from the pans. Let cool completely before slicing.
Variations
Many people associate rye bread with the licorice-like flavor of caraway because the seeds have been used for so long in deli-style rye breads. But for this type of loaf, caraway is only one of many optional add-ins, including aniseeds, black onion seeds (nigella seeds), poppyseeds, dried orange peel, fresh or dehydrated chopped onion, or nothing at all. The choice is yours.
