• Preheat oven to 200°C. Line a 20 cm pan with baking paper.
• In a medium saucepan, combine the butter, cocoa powder and vegetable oil over medium-high heat until it just comes to the boil. Remove from the heat and set aside to cool down slightly.
• Next, combine the sugars, eggs, buttermilk and vanilla in a large mixing bow
• Slowly whisk in the melted butter mixture.
• Add in flour, baking soda and salt, and stir just until combined. Fold in the white chocolate chips.
• Pour into lined tin and bake for 20 minutes. Set aside to cool down.

Buttermilk Chocolate Frosting

• Meanwhile for the frosting, add the butter, cocoa powder and buttermilk to a saucepan over medium-high heat and stir until combined.
• Transfer melted mixture to a mixing bowl and whisk in icing sugar gradually until the frosting is smooth and thick.
• Pour the frosting over the brownies (they don't have to be completely cooled yet) and smooth with an offset spatula.
• Put the frosted brownies in the fridge for a few hours until set, then cut into 16 squares and enjoy!