In a bowl, whisk together flour, sugar, baking powder, baking soda, and salt. In another bowl, combine buttermilk, egg, melted butter, and vanilla. Add the wet ingredients to the dry and mix until just combined. Do not overmix. In a small bowl, mix melted butter, brown sugar, and cinnamon. Pour into a zip-top bag or squeeze bottle. Heat a non-stick skillet over medium-low and grease lightly. Pour pancake batter onto the skillet. Once bubbles appear, swirl the cinnamon mixture on top. Flip and cook until golden and cooked through. Repeat with remaining batter. Whisk together glaze ingredients and drizzle over warm pancakes before serving.