Preheat your oven to 350°F (175°C) and line an 8-inch square baking pan with parchment paper, greasing lightly.

In a large bowl, whisk together the flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and cinnamon until well combined.

In another bowl, melt the unsalted butter and cool it, then whisk in maple syrup, milk, egg, and vanilla extract until smooth.

Fold the wet ingredients into the dry ingredients until just combined; the batter should be slightly lumpy.

Pour the batter into the prepared pan and spread it evenly, smoothing the surface with a spatula.

Bake for 20 to 25 minutes, checking for doneness with a toothpick.

Let the bars cool for 10 minutes in the pan, then transfer to a wire rack to cool completely before slicing.