Preheat your oven to 350°F (175°C) and line a 9x13-inch baking pan with parchment paper.

In a medium saucepan over low heat, melt butter and chopped chocolate until smooth.

Whisk granulated sugar into the warm chocolate mixture until fully dissolved.

Add eggs one at a time, whisking vigorously, then mix in cocoa powder, vanilla, and salt.

Fold flour into the brownie batter until no streaks remain.

In another bowl, cream together butter, granulated sugar, and brown sugar until fluffy.

Beat in the egg and vanilla until smooth, then mix flour, baking soda, and salt separately before combining with creamed mixture.

Spread the brownie batter into the prepared pan, dollop cookie dough on top, and swirl together.

Bake for 30-35 minutes, checking for doneness with set edges and a slightly jiggly center.

Cool in the pan for at least 45-60 minutes, lift out, and slice into squares.