To make the filling: Combine all of the dry ingredients in a small bowl. Add the melted butter and stir with a fork until the mixture looks like wet sand. Set aside.
Preheat the oven to 425 F. Brush a 9” cake pan with 1 tbs of the melted butter.
Dough: In a medium bowl, combine the flour, sugar, baking powder, baking soda, and salt. Add the buttermilk, syrup, and 2 tbs of the melted butter, and stir until just combined. Transfer the dough to a floured work surface and knead until smooth (it will still be very soft and a little sticky, but will be smoother and less lumpy). Place in a lightly floured bowl, cover, and chill for 20 minutes.
Once chilled, flatten the dough into a rectangle about 12 X 8 inches. Pour 2 tablespoons of the melted butter on and spread around with your fingers. Pour the filling over the dough and spread it evenly over the top, leaving about a 1/2 inch or so border around the outside edge. Press the filling down to pack it on top of the dough.
Starting on the long side of the dough, roll the side up, pressing as you go, to create a tightly rolled log (be gentle, as this will likely stick to the counter a bit). Pinch the seam closed and lay the log seam side down. Cut into 8 even pieces, and transfer each roll to the prepared cake pan. Brush with the remaining 2 tablespoons of melted butter. Bake for 20 to 23 min, until golden brown.
To make the icing: In a medium bowl, cream the butter and add the sugar. Mix until the sugar and butter start to come together a bit. Add the syrup and whisk well, until the mixture is smooth. If it is too thick, add a teaspoon or so of milk to loosen it up.
Allow cinnamon rolls to cool in the pan for about 5 min. Pour the icing over the rolls.
