A cinnamon swirl bread that's light, fluffy and incredibly yummy

Ingredients

• 3/4 cup whole milk, heated to about 115°F, plus more for the egg wash
• 1/4 cup granulated sugar, divided
• 1 tablespoon active dry yeast
• 2 large eggs, divided
• 1 teaspoon kosher salt
• 1/4 cup (160 grams) mashed russet potato (about 1 large potato, peeled, boiled, mashed, and cooled completely)
• 4 cups (480 grams) all-purpose flour
• 8 tablespoons (113 grams) butter, at room temperature, plus more for the pan
• 3/4 cup packed light brown sugar
• 2 teaspoons ground cinnamon

Directions

1. In the bowl of a mixer fitted with the dough hook, combine the milk, 1 teaspoon of the sugar, and the yeast. Let stand until foamy, about 5 minutes.
2. Add one egg and one egg yolk, salt, potato, and flour and knead the dough, on low, until it starts to come together, about 3 minutes. It will still look a little bit dry. Don't worry.
3. Add the butter, a piece or two at a time. It may look like it's not getting in there but don't worry, it will; just keep adding and kneading. (You might have to stop the mixer and knead the butter in with your hands for a minute to get it started.) Once incorporated, increase speed to medium and knead dough for another few minutes until it is smooth and elastic.
4. Form the dough into a nice ball, cover the bowl, and set aside to double. This could take 30 minutes or 2 hours, depending on how warm your house is. It's best to just keep an eye on it and watch the dough rather than the clock.
5. In a small bowl, combine the brown sugar and cinnamon. Cover and set aside. Butter two 8 1/2 -by- 4 1/2-inch loaf pans and line them with parchment, leaving a 2-inch overhang on the two long sides.
6. Tip the dough out onto a work surface. You shouldn't need flour at this point. Divide the dough in half. Cover one half while working with the other. Pat or roll one half of the dough out into an 8-inch-by-14-inch rectangle. Sprinkle evenly with half of the brown sugar mixture. Starting at one of the short edges, roll the dough up tightly and pinch the end to seal. Set the loaf in of the prepared pans, seam side down. Repeat with the remaining dough and filling. Cover the loaves and set aside to rise. It's ready to bake once the dough as come up about 1-inch over the edge. This step will take as long as it takes. Start preheating the oven to 350°F once the dough is about 1/2 inch above the edge of the pan.
7. Whisk the remaining egg white with a two teaspoons of milk and gently brush over the top of the loaf. Bake until deep golden brown and the internal temperature has reached 190°F, 30 to 35 minutes. Let cool on sheet on a wire rack for 20 minutes, then tip the loaves out of the pan and turn right side up to cool completely.