Make the brownie cookie dough:

1. In a small mixing bowl, add the butter and chopped chocolate. Place into the microwave and heat in 30 second intervals, stirring in between, until full melted and smooth. Set aside.
2. In a medium mixing bowl, whisk together the flour, sifted cocoa powder, baking soda, and salt, until very well-combined. Set aside.
3. In a large mixing bowl, add the egg, sugar, and vanilla. Using an electric hand mixer, beat together on high speed until the mixture looks very pale and fluffy, about 4 minutes.
4. Pour in the melted chocolate/butter mixture, then beat again until combined.
5. Add in the dry ingredients, then beat again until combined. Note that the batter will be more runny than cookie dough and liquidy. It will harden up once chilled. Fold in chocolate chips, if using.
6. Place the brownie cookie dough into the fridge to cool slightly while you make the chocolate chip cookie dough, about 15 minutes.

Make the chocolate chip cookie dough:

1. In a medium to large sized mixing bowl, whisk together the flour, baking soda, and salt, until well-combined. Set aside.
2. In a large mixing bowl, use a hand mixer or stand mixer cream together butter and sugars on medium speed until light and fluffy, about 2 minutes. Add egg and vanilla, and beat on low until incorporated. 
3. Add the dry mixture into the wet, then stir until fully-combined, then fold in the chocolate chips.
4. Use a small cookie scoop to scoop out the chocolate chip cookies (about 1 tablespoon full), and place onto one of the prepared baking sheets.

Assemble and bake:

1. Remove the brownie cookie batter from the fridge, then use the same cookie scoop to scoop out the brownie cookies, and place onto the same cookie sheet with the chocolate chip cookies.
2. Preheat the oven to 350F. Line 2 large baking sheets with parchment paper.
3. Return the cookie balls into the fridge and chill for 15 minutes while the oven preheats.
4. Take each chocolate chip cookie dough ball, and firmly press it together with a brownie cookie dough ball, then lightly roll it together to further form them together. Make 6 blended cookie balls, and place the rest back in the fridge to keep them cool.
5. Place the 6 cookies onto the second prepared baking sheet, then place into the oven to bake for 10-14 minutes. When done, the edges should look golden and the centres should look set. Note: It is best to work in batches while baking, while keeping the remaining cookies cold in the fridge between batches.
6. Repeat baking with remaining cookies.
7. Allow the cookies to cool on the baking sheet for 5 minutes, then carefully transfer them to wire cooling rack to cool.