Preheat the oven to 350ºF and line an 8-inch square baking dish with parchment paper.

In a medium saucepan over medium heat, melt the butter. Remove from the heat and stir in the cocoa powder until smooth and glossy. Whisk in both sugars. Add the eggs and vanilla, stirring until fully incorporated. Switch to a wooden spoon and stir in the flour, salt, and baking soda. Stir in the chocolate chips.

Pour batter into the prepared baking dish and bake for 25-30 minutes. Remove from the oven and allow to cool completely.

Preheat oven to 325ºF. In a medium saucepan over medium heat, melt the butter. Remove from the heat and whisk in the brown sugar until smooth. Add the corn syrup, eggs, vanilla, and salt, and continue whisking until combined. Stir in the pecans.

Pour mixture over the cooled brownies, and bake in the oven for 35-40 minutes or until golden and set. Cool completely before slicing into squares.