Preheat oven to 350°F (175°C). Grease a 9-inch pie dish or tart pan.

In a microwave-safe bowl, melt the chopped chocolate and butter in 30-second intervals until smooth. Let cool slightly.

In a large bowl, vigorously whisk the granulated sugar, brown sugar, and eggs for 3-4 minutes until pale and slightly thickened.

Slowly pour the melted chocolate mixture into the egg mixture, whisking gently until combined. Stir in vanilla.

Sift the cocoa powder, flour, and salt over the wet ingredients. Fold gently with a spatula just until no dry streaks remain.

Pour batter into the prepared pie dish and smooth the top.

Bake for 30-35 minutes until the edges are set and the center is slightly jiggly. Do not overbake.

Let cool completely on a wire rack for 1-2 hours before slicing.

Slice into wedges and serve with a heavy drizzle of chocolate syrup.