Preheat your oven to 350°F (175°C). Melt your 2 tablespoons of butter and pour it directly into an 8x8 or 9-inch square baking pan so it covers the bottom completely.
In a small bowl, whisk together the flour, baking soda, and salt. Toss in the chopped nuts to coat them, then set this dry mixture aside.
Mix Wet Essentials: In a separate bowl, whisk together the brown sugar, slightly beaten eggs, and vanilla extract until smooth and combined.
Gently fold the dry flour and nut mixture into the egg mixture until just combined into a thick batter.
Pour the batter directly over the melted butter in your baking pan. Crucial Tip: Do not stir! Let the batter sit right on top of the butter pool so it creates a caramelized crust as it bakes.
Bake at 350°F for 30 minutes until set and deeply golden.
Let the pan cool slightly, give the top a generous dusting of powdered sugar, and slice into 9 thick, chewy squares.