In a small bowl, whisk together the flour, cocoa powder, and sea salt. Set aside.

Melt the semisweet chocolate and butter in a microwave-safe bowl or over low heat on the stovetop. Stir until smooth and glossy. Set aside to cool slightly.

Beat the eggs in a standing mixer or with a handheld mixer for about 1 minute until pale and thick. Add the granulated sugar and beat for another minute.

Add the melted chocolate/butter mixture and vanilla extract to the eggs. Stir on low speed until smooth.

Add the dry ingredients to the wet mixture and stir on low speed until fully combined.

Spread the brownie batter evenly in the prepared pan.

Bake in the preheated oven for 25-30 minutes, or until the top is set but still slightly jiggly in the center.

Let the brownies cool completely on a wire rack.

In a standing mixer fitted with the paddle attachment, or with a handheld mixer, beat the butter, granulated sugar, and brown sugar for 1 minute until fluffy.

Add the milk and vanilla extract and beat until combined.

Stir in the flour, baking soda, baking powder, and salt, and beat until the dough comes together.

Fold in the mini chocolate chips. Set the cookie dough aside.

In a small saucepan, heat the heavy cream over medium heat until it simmers. Remove from heat and whisk in the chocolate chips and vanilla extract until smooth and glossy.

Allow the ganache to cool for 5-10 minutes, whisking occasionally.

Spread the cookie dough evenly over the cooled brownies. Be gentle to avoid pressing too hard.

Gently spread the cooled ganache over the cookie dough layer.

Place the brownies in the refrigerator for 2 hours, or until the ganache is fully set.

Remove from the refrigerator and cut into 16 squares. Serve at room temperature or slightly chilled.