For the Dough
¼ cup warm water (105° to 110°)
1 (0.25-ounce) package active dry yeast
3½ cups all-purpose flour
¼ cup sugar
1½ teaspoons kosher salt
¾ cup whole buttermilk
1 large egg, lightly beaten
6 tablespoons unsalted butter, softened

For the Filling
½ cup unsalted butter, softened
¾ cup firmly packed light brown sugar
2 tablespoons ground cinnamon

1/4 cup unsalted butter, softened
4 ounces cream cheese, softened
1 cups confectioners’ sugar
2 teaspoons vanilla extract

For dough:
In a small bowl, combine ¼ cup warm water and yeast. Let stand until mixture is foamy, about 5 minutes.
In the bowl of a stand mixer fitted with the paddle attachment, combine flour, sugar, and salt. With mixer on low speed, add yeast mixture, buttermilk, egg, and butter. Increase mixer speed to medium, 
and beat until dough comes together. Switch to the dough hook attachment. Continue beating until dough is smooth and elastic, about 7 minutes.
Spray a large bowl with cooking spray. Place dough in bowl, turning to grease top. Cover and let rise in a warm, draft-free place (75°) until doubled in size, about 1 1⁄2 hours.
Lightly punch dough down. On a lightly floured surface, roll dough into a 14×10-inch rectangle.

For filling:
Spread butter over dough. 
In a small bowl, stir together brown sugar and cinnamon. Sprinkle sugar mixture over butter; gently press mixture into dough. Starting with one long side, roll dough into a log; pinch seam to seal. Place log seam side down, and cut into 10 rolls.
Spray a 10-inch cast-iron skillet with cooking spray. Place rolls in prepared skillet. Cover and let rise in a warm, draft-free place (75°) until doubled in size, 45 to 60 minutes.
Preheat oven to 350°. Uncover rolls. 
Bake until golden brown and cooked through, 30 to 35 minutes. Let cool 
slightly in skillet.

For icing:
In a medium bowl, cream together room temperature butter and cream cheese. Add confectioners’ sugar and vanilla; whisk or beat until smooth. Spread glaze over warm rolls.