Toasted Meringue Hazelnut Blondies

Ingredients

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Preparation

1. Blondie

   Step 1

   Place a rack in middle of oven; preheat to 325°. Lightly coat a 9x9" pan with nonstick vegetable oil spray. Line pan with parchment paper, leaving overhang on two sides. Toast 2 cups blanched hazelnuts on a rimmed baking sheet, tossing halfway through, until golden brown and fragrant, 15–18 minutes. Let sit until cool enough to handle, then coarsely chop; set aside.

   Step 2

   Cook 1 cup (2 sticks) unsalted butter in a small saucepan over medium heat, stirring often, until butter foams, then browns (do not burn), 7–9 minutes. Remove from heat.

   Step 3

   Whisk 2 large eggs, room temperature, 1 large egg yolk, room temperature, 1¼ cups (250 g) granulated sugar, ¼ cup (packed; 50 g) light brown sugar, 2 tsp. vanilla bean paste or vanilla extract, 1½ tsp. Diamond Crystal or ¾ tsp. Morton kosher salt, and ¾ tsp. instant espresso powder (if using) in the bowl of a stand mixer fitted with the whisk attachment on medium-high speed until mixture is pale and doubled in volume, 6–9 minutes (mixture will form an unbroken ribbon when whisk is lifted from bowl).

   Step 4

   Reduce speed to low and with motor running, gradually pour in brown butter in a thin, continuous stream; beat until incorporated, about 2 minutes. Remove bowl from mixer and gently fold in 1½ cups (187 g) all-purpose flour with a rubber spatula, scraping down sides and bottom of bowl, until no large, dry streaks of flour remain. Scrape batter into prepared pan; smooth surface. Top with reserved hazelnuts and press in gently to adhere (surface will be smothered with nuts).

   Step 5

   Bake blondie until edges are golden brown and center is just set, 35–45 minutes. Transfer pan to a wire rack and let blondie cool in pan. Using parchment paper to help, lift blondie out of pan and transfer to rack.

2. Meringue and Assembly

   Step 6

   Meanwhile, combine 3 large egg whites and 1 cup (200 g) granulated sugar in the clean bowl of stand mixer and set over a saucepan of just simmering water (make sure bottom of bowl does not touch water). Heat, whisking constantly, until sugar is dissolved and an instant-read thermometer registers 170°.

   Step 7

   Fit bowl onto mixer fitted with clean whisk attachment. Beat egg white mixture until thick and glossy and mixture is barely lukewarm, 8–10 minutes. Add 1 tsp. vanilla bean paste or vanilla extract and ½ tsp. Diamond Crystal or ¼ tsp. Morton kosher salt; fold in with a rubber spatula just to combine. Taste meringue and season with more kosher salt if needed

   Step 8

   Peel away parchment paper from blondie and transfer to a heatproof platter. Using an offset spatula, spread meringue evenly over blondie, covering from edge to edge. Using a kitchen torch, toast meringue until deep golden brown. Sprinkle with flaky sea salt. Using a long knife and wiping off with a damp kitchen towel between cuts, slice blondie into 9 squares.

   Do Ahead: Blondie can be baked 24 hours ahead. Store, loosely covered, at room temperature.