Preheat oven to 350F and line an 8x8 pan with parchment paper.
Add eggs and sugar to a large mixing bowl and mix with an electric mixer. Mix until light and fluffy – about 3 minutes.
Chop chocolate bar into chunks and melt with butter in the microwave or over a double boiler. Only warm until the butter is just melted. Mix until evenly combined and pour chocolate and butter mixture into the eggs and sugar along with the vanilla extract. Mix again with the electric mixer.
Add cocoa powder, flour, and salt to the bowl and fold in with a spatula. Mix until the dry ingredients are just folded in.
Set batter aside and prep pecan layer. Whisk together melted butter, brown sugar, and vanilla extract. Fold in chopped pecans, cinnamon and salt.
Pour brownie batter into prepared pan and smooth into an even layer. Then, add the pecan layer in dollops on top of the brownie so that you can smooth into an even layer.
Place pan in the oven and bake at 350F for 35-40 minutes. Allow brownies too cool completely before cutting into squares