Preheat Oven: Set oven to 350°F (175°C). Grease a 9×13-inch baking pan or line with parchment paper.
Mix Dry Ingredients: In a large bowl, whisk together flour, granulated sugar, brown sugar, baking powder, baking soda, salt, cinnamon, and nutmeg.
Combine Wet Ingredients: In a separate bowl, whisk melted butter, eggs, buttermilk, maple syrup, and vanilla extract until smooth.
Combine Mixtures: Slowly fold wet ingredients into dry until just combined. Avoid overmixing for a soft, tender texture.
Pour Batter: Spread batter evenly in prepared pan using a spatula.
Bake: Bake for 25-30 minutes or until a toothpick inserted in the center comes out clean.
Cool: Allow bars to cool in the pan for 15-20 minutes, then transfer to a wire rack.
Slice and Serve: Cut into squares or rectangles and enjoy.