Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.
In a large bowl, beat the butter and brown sugar until creamy, scraping down the sides as you mix.
Add in the eggs and vanilla, and beat until well combined.
Mix in 4 cups of the flour, along with the baking soda, baking powder, and salt, until a dough forms.
Divide the dough evenly into two portions. Return one portion to the mixing bowl, beat in the remaining ¼ cup flour, and stir in 1 cup of chocolate chips.
For the second portion, add the cocoa powder and mix until fully blended, then beat in the remaining 1 cup of chocolate chips.
Using a cookie scoop, take a scoop from each dough (one chocolate, one cookie) and place them side by side on the baking sheet. Press together gently, shape into a circle, and flatten slightly. Repeat with the remaining dough.
Bake for 12–13 minutes, until the edges are set but the centers are still soft.
Remove from the oven and let cool on the baking sheet for 1 minute, then transfer to a wire cooling rack.