Preheat oven to 160°C. Generously grease an square or round tin, then line the base with parchment.
Gently melt the butter and chocolate together, either over a pan of simmering water or in the microwave. Stir until smooth and set aside.
In an electric mixer, over medium speed, beat sugar and eggs, one at a time, beating well after each addition. Add vanilla extract and continue beating until fluffy.
Using electric hand beaters, whisk the egg whites, and a pinch of salt until stiff but not dry. Set aside.
Pour the chocolate mix around the edge of the bowl with egg yolks and sugar mix, then fold together using a large wooden spoon until the batter is well combined.
Fold in the meringue into the bowl. Don't rush this bit. Fold it until even. Slowly pour the batter into the tin. Bake for 30 minutes and let it cool inside the oven.
The brownies may sink and crack a little, which is fine. Carefully cut into squares. Serve with whipping cream or ice cream, if desired.
