Preheat your oven to 350°F (175°C). Line a baking sheet with parchment paper.

Prepare the brownie cookie dough: In a medium bowl, cream together 1/2 cup softened butter and 1 cup white sugar until light and fluffy. Beat in 2 eggs one at a time, then stir in 1 teaspoon vanilla. Mix in cocoa powder, 1/2 teaspoon baking powder, and 1/4 teaspoon salt. Gradually stir in 1 cup flour until just combined. Fold in 1/2 cup chocolate chips. Set aside.

Make the chocolate chip cookie dough: In a separate bowl, cream together the remaining 1/2 cup softened butter with brown sugar and remaining white sugar until smooth. Beat in the remaining egg and vanilla. In another bowl, combine the remaining flour with baking soda and salt; gradually stir into the butter mixture. Fold in the remaining chocolate chips.

Form the cookies: Take a tablespoon of brownie dough and roll it into a ball. Do the same with the chocolate chip cookie dough. Press the two balls together and slightly flatten to create a two-toned cookie. Place on the prepared baking sheet, leaving about 2 inches between each cookie.

Bake in the preheated oven for 10-12 minutes, until edges are set but centers still appear slightly soft. The brownie side might look a bit underdone, but it will continue cooking as it cools.

Allow cookies to cool on the baking sheet for 5 minutes before transferring to a wire rack to cool completely (though they're divine when eaten warm!).