Preheat your oven to 350°F (175°C). This ensures your brownies bake evenly.
In a medium saucepan, melt 1/2 cup of butter with 3/4 cup of semi-sweet chocolate chips over low heat. Stir continuously until smooth and combined.
In another bowl, whisk together the cocoa powder, granulated sugar, baking powder, salt, and flour.
Once the chocolate mixture has cooled slightly, add in the eggs and 3/4 teaspoon of vanilla extract. Mix well. Gradually add the dry ingredients to the chocolate mixture and stir until just combined.
Pour the brownie batter into a greased 8x8 inch baking pan. Spread it evenly and place it in the preheated oven. Bake for 20-25 minutes or until a toothpick inserted comes out with a few moist crumbs.
While the brownies are baking, make the frosting. In a bowl, combine 3 tablespoons of softened butter, 3 tablespoons of cookie butter, and 1/2 teaspoon of vanilla extract. Mix until smooth, then gradually add in 1 cup of powdered sugar and 1 tablespoon of milk until the frosting reaches your desired consistency.
Once the brownies have cooled, spread the cookie butter frosting generously over the top. Cut into squares and enjoy your delicious Cookie Butter Brownies!