I heat the oven to 180 °C (fan 170 °C / about 356 °F) and line and grease my 20 cm square pan. Having the tin ready makes everything move smoothly once the batter is done.
I melt the butter, then beat in caster sugar and cocoa until smooth. After that I mix in the eggs, vanilla, and red colouring gel until the batter is glossy and even in colour.
I gently fold in the flour and salt, stir in white wine vinegar, pour into the tin, smooth the top, and bake for 23-25 minutes until edges look set and the top has a slight crust. Cooling completely in the tin is crucial before slicing. I sometimes melt white chocolate and drizzle it decoratively across the brownies for extra flair.