Grease and line a 22 cm (8.66 inches) brownie tin with parchment paper and vegetable oil.
Preheat oven to 160°C (320°F)(fan forced), or 180°C (356°F) non-fan forced oven.
Place the self-raising flour, cocoa powder, caster sugar, and salt in a large bowl. Mix until combined.
Place wet ingredients vegetable oil, vanilla extract, milk, condensed milk in a separate large to medium bowl. Mix well.
Melt the dark chocolate in the microwave in short bursts. Make sure to stir the chocolate between stopping the microwave. Allow the chocolate to cool slightly but not so that it becomes solid.
Add melted chocolate to the wet ingredients. Mix until combined.
Add the wet mixture to the dry ingredients and mix until combined. Do not over mix.
Place mixture in the prepared tin and flatten the top. It can help to gently tap the tin on the worksurface to flatten the top.
Add the chopped nuts on top if desired.
Bake for 35-40 minutes or until the brownie is cooked in the centre. You can test this by carefully poking a knife in the centre of the brownie. The brownie should have a moist crumb it should not have the same consistency as the wet batter.
Allow the brownie to cool in the tin for 10 minutes, then remove from tin and transfer to a wire rack. Serve.
Notes
The brownie will double in size. If you have a shallow tin, raise the sides with some foil.
If it looks like it is going too brown on top but it is not yet cooked, carefully place some foil loosely on the top of the brownie.