Instructions

• Preheat the oven to 350°F (175°C). Line a 9×9-inch metal baking pan with parchment paper leaving an overhang on two sides, or lightly grease the pan; set aside.
• Put 3/4 cup unsalted butter in a medium saucepan and melt over medium heat. Once melted, increase the heat slightly (a notch above medium) and continue cooking, stirring constantly.
• Watch the butter as it pops and sizzles; when the milk solids turn golden brown and the butter is fragrant, immediately remove the pan from the heat.
• Pour the browned butter into a large heatproof bowl. Let it cool until warm but not hot, about 20 minutes (this prevents the eggs from cooking when added).
• Add 1 cup packed brown sugar and 1/3 cup granulated sugar to the cooled browned butter and mix until combined.
• Whisk in 1 large egg plus 1 egg yolk (both at room temperature) and 1 1/2 teaspoons vanilla extract until smooth and well combined.
• Add 1 1/4 cups all-purpose flour and 3/4 teaspoon salt to the wet mixture and stir until just combined (do not overmix).
• Fold in 1/3 cup chopped walnuts and 1/2 cup toffee bits until evenly distributed.
• Spread the batter evenly into the prepared 9×9 pan, smoothing the top with a spatula.
• Bake for 20–25 minutes, until the edges are golden brown and a toothpick inserted into the center comes out mostly clean with a few moist crumbs. Start checking at 20 minutes.
• Remove the pan from the oven and place it on a wire rack. Let the blondies cool completely in the pan, then lift them out using the parchment overhang (if used) and cut into squares before serving.