Preheat the oven to 160°C fan / 180°C conventional. Line a 20cm square baking tin with baking paper.
In a glass bowl or jug, add the dark chocolate and butter. Microwave in 30-second blasts, stirring in between, until smooth and melted. Set aside to cool.
120 grams 70% dark chocolate, 150 grams Unsalted butter
In a separate bowl, whisk the caster sugar and eggs for a couple of minutes until pale in colour, thick and foamy.
2 medium Eggs, 220 grams White caster sugar
Add the vanilla extract, white wine vinegar, melted chocolate and red food colouring to the whisked eggs. Fold everything together until the mixture is smooth and bright red.
2 teaspoon Vanilla extract, 1 teaspoon White wine vinegar, 1-2 teaspoons Red food colouring (gel or oil-based)
Sift in the flour and cocoa powder, then fold together until the brownie mixture is just combined.
130 grams Self-raising flour, 20 grams Cocoa powder
Spoon into the baking tin and spread out evenly. Bake for 22-25 minutes until the brownies are set on top, small cracks appear on the outer edges, and the middle has a slight wobble to it.
Leave to cool completely for at least 3-4 hours or overnight for best results (this will allow the brownies to set and turn fudgy). You can speed up the cooling time by refrigerating the brownies for 2 hours instead.