Fudge Chocholate Brownii

Ingrediants:

• 125g (1/2 cup) unsalted butter, plus more for greasing the pan
• 125g (4.4 oz) dark chocolate (around 60% cocoa), roughly chopped
• 335g (1 1/2 cups) white sugar
• 3 large eggs, at room temperature
• 1 tsp vanilla extract
• 115g (3/4 cup) all-purpose flour
• 30g (1/4 cup) Dutch-process cocoa powder
• 1/2 tsp salt
• 1 cup (180g) semi-sweet chocolate chips (optional)