Adjust oven rack to middle position and preheat oven to 425 degrees. Line a 9×9 pan with aluminum foil and brush with one tablespoon butter.
Combine brown sugar, 3 tablespoons sugar, cinnamon and 1/8 teaspoon salt in a small bowl. Add one tablespoon melted butter and stir until crumbly. Set aside.
In a large bowl, whisk together flour, 2 tablespoons sugar, baking powder, baking soda and 1/2 teaspoon salt. Add 3 tablespoons of the melted butter and buttermilk to the dry ingredients and stir until the liquid is absorbed (dough will still be sticky), about 30 seconds.
Transfer dough to a lightly floured work surface. Knead until just smooth, about 30 seconds. Try not to over-knead as it can make it doughy. Lightly dust the surface with flour again. Pat the dough into a small rectangle, then roll into a 12-inch x 9-inch rectangle. Brush the dough with 1 tablespoon of melted butter then sprinkle the brown sugar filling evenly over the dough, leaving a 1/2-inch border. Press the filling firmly into the dough with your hand.
Starting at the long side, roll the dough to form a tight log. Pinch the seam to seal. Roll the log seam-side down and cut into 9 pieces using a serrated knife or a piece of thread. Slightly flatten each piece on its flat side to seal the open edges. Place the rolls in prepared pan and brush with remaining tablespoon of butter. Bake until the edges are golden brown, 23-25 minutes.
Meanwhile, make the glaze by whisking cream cheese and buttermilk together until smooth. Add the powdered sugar and mix until a thick glaze forms.
When the rolls are done, lift them out of the baking pan and onto a wire rack. Cool for 5 minutes, then carefully separate the buns, using a knife if necessary. Drizzle the glaze evenly over the buns. Serve warm.