Preheat oven to 350°F. Line an 8-inch x 8-inch baking pan with parchment paper and set aside.
In a small bowl, whisk together flour, baking powder and salt; set aside.
Melt butter in a small saucepan over medium-low heat. Cook, stirring often, as butter foams and then begins to brown and smell nutty, 5-8 minutes. When golden brown, remove from heat to cool slightly.
Whisk brown sugar and maple syrup into the browned butter. Add egg, egg yolk, and vanilla and whisk smooth. Mix in dry ingredients until just combined. Gently fold in pecans.
Pour batter into prepared pan and smooth the surface. Bake for 22-25 minutes, or until the blondies are golden brown and the edges have set, but the center is still soft. Let cool. Drizzle with maple icing (recipe below). Cut into squares and enjoy.
Whisk together melted butter and maple syrup in a medium bowl. Add powdered sugar and a pinch of salt and whisk until smooth and glossy. Use right away.
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