Nutella-Stuffed Brown Butter Blondies

• Preheat your oven to 350°F (175°C). Line your 9x13-inch baking pan with parchment paper, leaving some overhang for easy removal later.
• In a medium saucepan over medium heat, melt the unsalted butter. Continue cooking, swirling the pan occasionally, until golden brown with a nutty aroma. Remove from heat and let cool slightly.
• In a large mixing bowl, combine the brown sugar and browned butter. Whisk until well combined. Add eggs, egg yolk, and vanilla extract; whisk until smooth.
• In a separate bowl, whisk together the all-purpose flour, baking powder, and kosher salt. Gradually add dry ingredients to wet mixture, stirring until just combined.
• Gently fold in the semisweet chocolate chunks and coarsely chopped hazelnuts until evenly distributed.
• Spread half of the blondie batter into the prepared pan. Dollop Nutella evenly over batter, then spread remaining batter on top, covering Nutella.
• Bake for 25-30 minutes until edges are golden brown and a toothpick inserted comes out with a few moist crumbs.
• Remove from oven and cool in pan for at least 10 minutes. Use parchment overhang to lift blondies out and cool completely on wire rack. Sprinkle with Maldon flake sea salt before serving.