Toast Pecans: Preheat oven to 350°F. Spread pecans on a sheet pan in a single layer. Toast for 6-8 minutes then set aside to cool.
Make Brown Butter: Melt butter in a heavy 2-quart saucepan over medium-high heat. Once melted, lower heat to medium and continue cooking, watching closely, for 6-8 minutes or until butter foams and turns deep golden brown or amber in color. Immediately remove from heat; pour into a medium size mixing bowl. Chill in the refrigerator for 15 minutes. (This will speed up the process.)
Make Blondies: Preheat oven to 350°F. Line a 13 x 9-inch baking pan with heavy duty aluminum foil, extending foil 2 inches over edges of pan. Spray bottom and sides of the foil-lined pan with cooking spray; set aside.
To the cooled brown butter add brown sugar, eggs and vanilla .Whisk by hand or using a hand mixer on low speed. Add flour, baking powder and salt; mixing just until fully combined.
By hand, stir in pecans and white chocolate chips. Spread into prepared pan.
Bake 25-30 minutes or until golden brown around edges and a toothpick inserted in center comes out clean. Cool completely in pan on a wire rack.
Use foil "handles" to lift blondies from pan. Cut into squares.
Store at room temperature in an airtight container for up to 3 days.