Preheat your oven to 425°F (220°C). Grease a 9×13-inch baking dish.

In a large mixing bowl, combine the flour, sugar, baking soda, baking powder, buttermilk, salt, 4 tablespoons of the melted butter, and vanilla extract. Stir or beat until just combined—don’t overmix.

In a separate bowl, mix together the brown sugar, cinnamon, and 2 tablespoons melted butter until well combined.

Turn the dough out onto a lightly floured surface and knead gently a few times. Divide the dough in half. Roll each half into a rectangle about ¼ inch thick.

Sprinkle half of the filling evenly over each dough rectangle. Roll each rectangle tightly lengthwise into a log. Trim the ends of each log, then slice each log into 12 even pieces.

Place the cinnamon rolls cut-side down in the prepared baking dish. Brush the tops with the remaining melted butter.

Bake for 20 minutes or until the rolls are lightly golden brown. Remove from the oven and let cool for 20 minutes.

While the rolls are cooling, beat together the cream cheese, powdered sugar, and 2–4 tablespoons of buttermilk until smooth. Spread the icing over the warm rolls before serving.