Preheat the Oven: Preheat your oven to 160ºC. Line a 9 x 13 baking pan with greaseproof baking paper.
Brown the Butter: In a medium saucepan over medium-low heat, melt the butter. Continue cooking until the butter turns golden brown and releases a nutty aroma, about 5 minutes. Set aside to cool.
Mix Wet Ingredients: Once the butter is cool, pour it into a medium mixing bowl. Add the vegetable oil, caster sugar, brown sugar, eggs, vanilla extract, and salt. Whisk until well combined.
Combine Dry Ingredients: Add the flour and cocoa powder to the wet mixture. Fold in gently until just combined.
Add Chocolate and Pecans: Stir in the chopped dark chocolate. Pour the batter into the prepared baking pan and sprinkle the chopped pecans evenly on top.
Bake: Bake in the preheated oven for 20-25 minutes until the top is shiny and crackly, and just set.
Cool and Slice: Remove from the oven and let the brownies cool in the pan for at least 30 minutes before slicing.