Preheat the oven to 375°F. Line an 8-inch square baking pan with parchment paper and spray with nonstick cooking spray.
Melt the butter and chocolate in the top of a double boiler placed over simmering water, stirring until completely smooth. Remove from the heat and set aside to cool.
Whisk together the eggs, sugar, and vanilla extract in a large bowl. Whisk together the flour and salt in a small bowl. Whisk the melted chocolate and flour mixture into the egg batter, mixing just until combined. Stir in the chocolate chips and pecans.
Pour the batter into the prepared pan and smooth the top. Bake for about 30 minutes, until a cake tester comes out clean. Remove from the oven and let cool completely on a wire rack.