Step 1

Place 6 tablespoons unsalted butter (4 for the dough, 2 for the filling), 1/2 cup buttermilk, and 1 large egg on the counter. Let sit at least 1 hour to come to room temperature.

Step 2

Place 1 cup all-purpose flour, 1/2 cup plus 2 tablespoons bread flour, 2 tablespoons granulated sugar, 1 1/4 teaspoons instant yeast, and 3/4 teaspoon kosher salt in the bowl of a stand mixer fitted with the paddle attachment. Beat on low speed until combined. Add the buttermilk, egg, and 2 tablespoons of the softened butter. Beat on low speed until a sticky dough forms, about 30 seconds.

Step 3

Replace the paddle with the dough hook and knead on medium-high speed until the dough is smooth and sticks to the bottom of the bowl and only a little to the sides, 3 to 5 minutes. If the dough is still quite sticky after 3 minutes, add an additional tablespoon or two of bread flour.

Step 4

Remove the dough from the bowl, grease the bowl with 1 tablespoon of the softened butter and return the dough to it, turning to coat. Cover with plastic wrap and let the dough rise until almost doubled in size, 1 to 1 1/2 hours. Meanwhile, make the filling.

Step 5

Place 1 1/2 cups cranberries, 6 tablespoons granulated sugar, 6 tablespoons water, and 1/8 teaspoon kosher salt in a small saucepan. Cook over medium-high heat, stirring occasionally, until the sugar dissolves, the cranberries begin to burst, and the mixture bubbles, 6 to 8 minutes. Simmer until thickened, about 5 minutes more.

Step 6

Remove from the heat and stir in 2 teaspoons vanilla extract. Let cool to room temperature.

Step 7

Coat an 8-inch round baking pan with 1 tablespoon of the softened butter. Line the bottom with a parchment paper round. Transfer the dough to an unfloured work surface. Roll out the dough into a 10-by-14-inch rectangle with a long side closer to you.

Step 8

Spread the remaining 2 tablespoons softened butter onto the dough, leaving a 1-inch border. Spread the cranberry filling over the butter. Starting with the long side nearest to you, roll the dough away from you to create a long cylinder. Pinch the dough together along the seam. The dough will be very wet and soft — don’t worry.

Step 9

Arrange the cylinder seam-side down. Cut crosswise into 8 pieces. Place cut-side up in the prepared pan. You may need to re-pinch the seam closed on each bun as you transfer them.

Step 10

Loosely cover the pan with plastic wrap. Let the buns rise until they are about 1 1/2 times their original size, 30 to 45 minutes. Meanwhile, arrange a rack in the middle of the oven and heat the oven to 350ºF.

Step 11

Whisk 1 large egg and a pinch of kosher salt in a small bowl. Uncover and brush the buns with the egg wash. Bake until nicely browned and the tip of a sharp knife stuck between two buns comes out clean, or a digital thermometer registers 200°F, 25 to 30 minutes. Meanwhile, make the glaze.

Step 12

Place 1 cup powdered sugar, 1 to 2 tablespoons buttermilk, 1 teaspoon vanilla extract, and 1/4 teaspoon kosher salt in a small bowl and whisk to combine.

Step 13

Let the buns rest in the pan on a wire rack for 10 minutes. Invert them onto the rack, and then transfer them right-side up onto a serving plate. Drizzle with the glaze and serve warm.