Preheat the oven to 350 degrees F (175 degrees C).

In a large bowl, combine 2/3 cup flour, cocoa powder, 1/4 teaspoon salt, and 1/4 teaspoon baking powder.

In a separate large bowl, stir together 3/4 cup sugar, coffee liqueur (optional), 2 eggs, and 1 teaspoon vanilla extract.

Add melted butter to the sugar mixture and then add the flour mixture; stir until just combined.

Spread the brownie batter into an ungreased 9x13-inch baking pan.

In a large bowl, sift together 1 1/3 cups flour, baking soda, 1/2 teaspoon baking powder, and 1/4 teaspoon salt.

In another large bowl, beat peanut butter, unsalted butter, brown sugar, and 1/2 cup white sugar together using an electric mixer until creamy.

Stir in 1 egg and 1 teaspoon vanilla extract into the peanut butter mixture.

Place cookie dough on top of the brownie mixture in the baking pan.

Bake in the preheated oven until the cookie layer is golden brown, 18 to 20 minutes.

Let cool for 15 minutes.

Cut into squares and leave in the pan until fully cool, about 20 minutes more.

Place white chocolate in a microwave-safe bowl.

Heat in microwave until melted, about 30 seconds.

Place melted chocolate in a resealable plastic sandwich bag and cut a very tiny hole in a corner.

Drizzle white chocolate over cooled cookie brownies.