This eye catching rhubarb and braided cinnamon bread is as beautiful as it is delicious. It's only very mildly sweet, and delightfully tart, so I recommend topping it with a vanilla glaze for a little extra sweetness!
For the bread dough, mix together the milk and yeast and allow to rest at room temperature for 5 minutes.
In the bowl of a stand mixer fitted with the dough hook attachment, mix together the flour, water, sugar, cinnamon, vanilla extract, salt, and milk mixture at low speed until the dough just barely comes together. It's ok if the dough is a bit bit shaggy before you add the butter, it will come together better once the butter is added in the next step.
Add the butter in three increments, mixing well after each addition. Continue mixing until a smooth dough forms and the dough pulls away from the sides of the mixing bowl, forming a smooth solid mass of dough around the hook, which takes about 5 minutes. (You can also do this by hand, just knead the dough until it's smooth and supple.)
Transfer the dough to a greased bowl, cover, and let it rise for 45 minutes at room temperature out of direct sunlight.
Divide the dough into 4 equally-sized pieces, about 6.5 to 7 ounces each, and knead each for a couple minutes to form a smooth ball. Pat each one into a rough rectangle shape, cover, and allow them to rest in the refrigerator for 90 minutes.
Meanwhile, you can begin to prepare the filling. In the bowl of a stand mixer fitted with the paddle attachment, cream together the butter and the sugar at medium speed until smooth and slightly fluffy. Add the egg white and mix until combined. Add the cinnamon, cardamom, salt, and vanilla and continue mixing until smooth. Add the flour last, and mix until *just* combined. Set aside.
Take one of the rectangles of dough and roll it out into a roughly 8 x 11-inch rectangle. Spread it with 1/4 of the filling mixture, then roll it up along the longest edge as you would if you were making cinnamon rolls. Roll the cylinder back and forth against the surface to lengthen it to 14 inches. Cover the roll in plastic wrap and place it in the refrigerator. Repeat with the remaining three rectangles of dough, and allow the rolled-up dough cylinders to chill in the refrigerator for 30 minutes.
To form the bread, cut each of the cylinders in half vertically with a pizza cutter. Transfer the strips, cut side facing up, to a baking sheet that has been lined with parchment paper, except for one strip. You can roll the extra strip into a spiral and set it aside on a small baking sheet or cake pan to bake a little cinnamon roll for yourself.
On the baking sheet, you should have 7 strips of dough, with the cut side facing up. Fold back every other strip. Place a rhubarb stalk on the flat strips, then place the folded strips back over the rhubarb, starting a weave pattern. Next, fold back the opposite strips over the rhubarb stalk and place a second rhubarb stalk down. Continue to weave all eight stalks of rhubarb into the bread in this manner. You can also watch the video right above the recipe for reference.
When you've woven in all the rhubarb, cover the loaf with a greased piece of plastic wrap and allow the dough to rise for 30 minutes at room temperature.
Preheat oven to 375 degrees Fahrenheit. Lightly brush the bread with an egg wash and then place in the oven. Bake uncovered until the bread is golden, about 40 to 45 minutes, then tent the loaf with tin foil cook and continue cooking until the internal temperature of the bread is 190 Fahrenheit, about 5 to 15 minutes more. Remove from the oven and allow to cool to room temperature.
While the bread is cooling, you can prepare the glaze. Whisk together the powdered sugar, milk, butter, and vanilla extract until smooth. Drizzle over the bread, slice, and serve.