How to Make It
Preheat oven to 350°F. Melt butter in a medium saucepan over medium. Cook, whisking constantly, until butter browns and smells nutty, 5 to 7 minutes. Immediately pour into a bowl. Place in refrigerator to cool, whisking every 5 minutes until thickened and creamy, about 20 minutes. (Butter should look like melted peanut butter.)
Beat eggs and sugar with an electric mixer on medium speed until thickened and pale yellow, about 3 minutes. Whisk together flour, baking powder, and salt in a bowl. Add to egg mixture in thirds, alternately with cooled butter, beginning and ending with flour mixture, beating on low after each addition. Slowly beat in maple syrup; add vanilla, and beat just until combined. Fold in 1 cup of the pecans with a spoon.
Pour batter into a greased and floured 13- x 9-inch baking pan, and spread into an even layer. Sprinkle with remaining 1⁄4 cup pecans.
Bake in preheated oven until golden and a wooden pick inserted in middle comes out clean, about 35 minutes. Transfer pan to a wire rack to cool completely, about 1 hour. Cut into 24 bars.