Preheat your oven to 180 degrees C (or 160 degrees C for fan ovens) and line a 9x9 inch square tin with parchment paper.

In a microwave-safe bowl, combine the dark chocolate and 200 g unsalted butter. Heat until smooth, then let it cool for 5-10 minutes.

In a separate bowl, whisk together the light brown soft sugar and 4 medium eggs until they’re doubled in volume and mousse-like.

Gently fold the cooled chocolate and butter mixture into the egg and sugar mixture.

Gradually fold in the plain flour and cocoa powder until just combined.

Pour this brownie mixture into your prepared tin and bake for 25 minutes.

Meanwhile, in a saucepan over low heat, melt together 50 g unsalted butter, 115 g light brown soft sugar, and 75 g golden syrup until smooth. Allow it to cool for 5 minutes.

Stir in the chopped pecans, 1 egg, sea salt (if using), and vanilla extract into the butter mixture.

Carefully pour the pecan topping over the partially baked brownies.

Return to the oven and bake for an additional 20-25 minutes until golden and bubbly.

Let cool in the tin, then refrigerate for at least 3 hours before slicing and serving.