Preheat oven to 325°F. Lightly coat a 13x9" glass baking dish with nonstick spray.
Cook butter in a medium saucepan over medium-low heat, stirring often, until it foams, then browns, about 5 to 8 minutes. Transfer to a large bowl; let cool slightly.
Add sugar to melted butter and whisk until smooth. Whisking constantly, add egg yolks one at a time followed by whole egg, beating after each addition to fully incorporate before adding more.
Whisk buckwheat flour, almond flour and salt in a medium bowl. Add dry ingredients to butter mixture and mix until smooth.
Add pecans and chocolate chips and mix until just incorporated.
Scrape batter into prepared dish; smooth top.
Bake blondies until lightly browned and center is firm when gently pressed, 20 to 25 minutes. Transfer dish to a wire rack and let cool.