1 3/4cups(12 ounces) dark brown sugar, tightly packed
1tablespoonpure vanilla extract
8ouncesgianduja chocolate, roughly chopped into 1- and 2-inch chunks
First, brown the butter. Place 1 cup unsalted butter into a lightly colored, heavy-bottomed pan over medium-low heat. Melt the butter, swirling the pan occasionally, until the butter starts to foam and splatter. Use a heatproof rubber spatula to scrape the sides and the bottom of the pan occasionally to prevent the butter from burning. After around 5 minutes, golden flecks should appear in the butter, and the butter should smell nutty and toasted. When scooped into a white plate, the butter should be a light to dark brown amberish color. Remove from heat and allow to cool to room temperature completely on a wire rack.
Once the butter has cooled, it's time to make the blondies! Center a rack in the oven and preheat to 350 (F). Prepare an 8 by 8-inch square baking pan by spraying with a light coating of cooking spray. Line the bottom and sides of the pan with parchment paper (Food52 has a great guide on how to do this perfectly). Set aside.
In a medium bowl, whisk together 1 1/2 cups all-purpose flour, 1/2 cup hazelnut meal, and 1 1/2 teaspoons kosher salt until well combined. Set aside.
In the bowl of a freestanding electric mixer fitted with a paddle attachment, combine 1 3/4 cups dark brown sugar, 2 large eggs, and 1 tablespoon pure vanilla extract. Beat on medium speed for 2 minutes, before lowering the mixer speed to its lowest setting and streaming in the cooled brown butter (from the 1st step). Continue mixing until the ingredients are well combined and a pretty, amber color, before adding the dry ingredients (from the 3rd step) all at once and beating until just combined. At this point, it's okay to have a couple flour streaks still visible in the batter.
Remove the bowl from the freestanding electric mixer and scatter 8 ounces chopped gianduja chocolate over the batter. Use a heatproof rubber spatula to hand mix the chocolate into the batter.
Once the chocolate is evenly distributed, transfer to the prepared baking pan and use an offset spatula to smooth the top. Bake in the preheated oven for 30 to 35 minutes, or until the edges of the blondies are set but the center still looks a little gooey (the blondies will continue to cook in the pan). Allow to cool on a wire rack slightly before consuming in all their delicious glory. Don't forget the milk!