Move an oven rack to the bottom third of the oven and preheat to 425 degrees. Line 1 muffin tin with 12 liners.
In a small bowl, microwave 4 tbsp butter and the maple syrup at high power until melted, about 30 seconds.
In a small bowl, mix together 1/3 cup granulated sugar, brown sugar, and cinnamon.
In a food processor, combine the flour, baking powder, the remaining 2 tbsp of granulated sugar, and salt. Pulse until well combined. Cut the remaining butter into small pieces and pulse together until the mixture resembles bread crumbs.
Pulse in the buttermilk until the dough comes together.
Transfer to a floured work surface, and pat dough into a 10" square. Use a pizza cutter or sharp knife to quarter the dough, then cut each quarter into 16 equal pieces. Roll into balls.
Dip each ball in the maple butter, then the sugar mixture. Place 4-5 coated balls into each muffin cup press down gently.
Tent the muffin tin with tin foil and bake until cooked through and golden, about 15-17 minutes.
Mix together confectioners sugar and milk to make the glaze. While the muffins are still warm, drizzle the glaze over the muffins. Serve warm.