In a medium saucepan over medium heat, combine the chopped chocolate and butter and stir until melted. Set aside to cool for around 10 minutes.
After 10 minutes have passed, in the same pot whisk in the sugar until combined, then the eggs and vanilla until combined.
Switch to a spatula and gently fold in the flower, cocoa powder and salt until just combined.
Stir in the chocolate chips and cocoa nibs if using, until just combined.
Pour batter into a greased oven safe skillet (9-12 inches) and bake at 180 C (350 F) for 25-35 minutes until a toothpick inserted in thecenter comes out with some moist crumbs. Don't overbake, so start checking early!