Preheat your oven to 350°F (175°C) and grease a 9x13-inch baking pan or line it with parchment paper.
In a large mixing bowl, whisk together the flour, granulated sugar, baking powder, salt, and cinnamon until well combined.
In another bowl, mix the melted butter, buttermilk, eggs, and vanilla extract until smooth.
Pour the wet ingredients into the dry ingredients and stir until just combined. Be careful not to overmix.
Spread the batter evenly into the prepared baking pan.
Bake for 20-25 minutes, or until a toothpick inserted into the center comes out clean.
While the bars are baking, prepare the maple glaze by whisking together the maple syrup and powdered sugar in a small bowl until smooth.
Once the bars are done baking, let them cool in the pan for about 10 minutes before transferring them to a wire rack.
Drizzle the maple glaze over the warm bars and allow it to set for a few minutes before slicing into squares.