Preheat the oven to 350°F (175°C) and line an 8×8-inch baking pan with parchment paper.
Whisk the melted butter and brown sugar together until smooth.
Add the maple syrup, egg, and vanilla extract and whisk until well combined.
In a separate bowl, combine the flour, baking powder, salt, and cinnamon.
Gradually add the dry ingredients to the wet mixture and stir just until combined.
Fold in the chopped walnuts evenly.
Spread the batter into the prepared pan and smooth the top.
Sprinkle additional chopped walnuts over the surface if desired.
Bake for 23–27 minutes, until the edges are golden and the center is just set.
Let the blondies cool completely in the pan before slicing into squares.
Drizzle with additional maple syrup before serving if desired.
