Preheat your oven to 350°F (175°C). Line an 8-inch square baking pan with parchment paper, ensuring there’s some overhang for easier removal later. Lightly grease the parchment paper to prevent sticking.
In a large mixing bowl, whisk together the all-purpose flour, granulated sugar, brown sugar, baking soda, baking powder, salt, and ground cinnamon until well combined.
In another mixing bowl, whisk together the melted unsalted butter, pure maple syrup, milk, large egg, and vanilla extract until everything is well blended.
Pour the wet ingredients into the bowl containing dry ingredients. Stir gently with a spatula until just combined—be careful not to overmix as this can lead to denser bars instead of soft ones.