Preheat oven to 350°F. Line a 9x13 inch baking pan with parchment paper.
Melt butter and chopped dark chocolate in a heavy-bottomed saucepan until smooth.
Whisk in the sugar, followed by the eggs and vanilla extract.
Gently fold in the flour, cocoa powder, and salt until just combined.
For the caramel: Melt the sugar in a saucepan, then whisk in butter, heavy cream, vanilla, and sea salt until smooth.
Spread brownie batter in prepared pan, swirl in caramel sauce, and sprinkle chopped pecans over the top.
Bake for 32–35 minutes until the center is just set.
Cool on a wire rack for at least 2 hours before slicing into squares.