Preheat oven to 425 degrees. Brush a 9-inch cake or pie pan with 1 Tbsp melted butter, set aside. In a mixing bowl whisk together 2 1/2 cups flour, 2 Tbsp granulated sugar, baking powder, baking soda and 1/2 tsp salt, set aside.
In a separate mixing bowl whisk together light-brown sugar, remaining 1/4 cup granulated sugar, cinnamon, nutmeg and 1/8 tsp salt. Add in 1 Tbsp melted butter and blend mixture together with your fingertips or a fork until mixture is well blended and evenly moistened, set aside.
Measure out buttermilk into a liquid measuring cup and stir in 2 Tbsp melted butter. Add buttermilk mixture to flour mixture and mix with a wooden spoon until a shaggy dough forms and liquid has been absorbed. Then, knead mixture in bowl by hand just until smooth, about 30 seconds - dough will be sticky but if it's too sticky to work with add in more flour, up to 1/2 cup as needed.
Sprinkle a clean work surface with a fair amount of flour. Pat the dough with your hands into a 12 x 9-inch rectangle. Brush top of dough with 2 Tbsp melted butter then sprinkle evenly with brown sugar mixture, coming within a 1/2 inch of the border on all sides. Press the brown sugar filling into the dough (they stated "firmly press" in their recipe which didn't make sense to me because then you are flattening your dough and releasing some of the rise the baking powder has already given so I only lightly pressed). Starting on the long side, roll dough (using a bench scraper or metal spatula to loosen dough from work surface if necessary. I didn't need one) snugly and gently to opposite end. Pinch the end seam to seal. Roll the log seam side down and cut dough into 8 equal portions.
Place 1 roll in the center of the prepared baking dish, then place remaining 7 rolls around it. Brush tops of rolls with remaining 2 Tbsp butter. Bake in preheated oven 22 - 25 minutes until edges are golden brown. (After baking you can invert the rolls using a plate onto a wire rack but I just served them without flipping). Serve warm drizzled with Cream Cheese Glaze. Store in an airtight container and reheat in microwave if desired.
Cream Cheese Glaze
In a mixing bowl, using an electric hand mixer set on medium speed, blend together cream cheese and butter until well combine and slightly fluffy, about 1 minute. Add in remaining ingredients and mix until well combine. Store in an airtight container.
Recipe Source: Cinnamon Roll - adapted from The Quick Recipe, By the Editors of Cook's Illustrated. Fastest Cinnamon Buns, pg 375 - 376.
Cream Cheese Glaze - Cooking Classy