Adjust oven rack to upper-middle position and heat to 425 degrees.
Pour 1 tablespoon melted butter in 9-inch nonstick cake pan; brush to coat pan.
Spray wire rack with nonstick cooking spray; set aside.
To make cinnamon-sugar filling:
Combine sugars, spices, and salt in small bowl.
Add 1 tablespoon melted butter and stir with fork or fingers until mixture resembles wet sand; set filling mixture aside.
To make biscuit dough:
Whisk flour, sugar, baking powder, baking soda, and salt in large bowl.
Whisk buttermilk and 2 tablespoons melted butter in measuring cup or small bowl.
Add liquid to dry ingredients and stir with wooden spoon until liquid is absorbed (dough will look very shaggy), about 30 seconds. Transfer dough to lightly floured work surface and knead until just smooth and no longer shaggy.
Pat dough with hands into 12 by 9-inch rectangle. Brush dough with 2 tablespoons melted butter. Sprinkle evenly with filling, leaving 1/2-inch border of plain dough around edges. Press filling firmly into dough. Starting at long side, roll dough, pressing lightly, to form a tight log. Pinch seam to seal. Roll log seam-side down and cut evenly into eight pieces. With hand, slightly flatten each piece of dough to seal open edges and keep filling in place.
Arrange buns in buttered cake pan.
Brush with 2 tablespoons remaining melted butter.
Bake until edges are golden brown, 23 to 25 minutes.
Use metal spatula to loosen buns from pan; without separating, slide buns out of pan onto greased cooling rack.
Cool about 5 minutes before icing.
To make icing and finish buns:
While buns are cooling, line rimmed baking sheet with wax paper(for easy cleanup); set rack with buns over baking sheet.
Whisk cream cheese and buttermilk in large nonreactive bowl until thick and smooth (mixture will look like cottage cheese at first).
Sift confectioners’ sugar over cream cheese mixture.
Whisk until smooth glaze forms, about 30 seconds.
Spoon glaze evenly over buns and serve immediately.