Ingredients

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