Preheat oven to 350°F.

Line bottom with (2) 9”x13” cake pans with parchment paper (see note); set pans aside.

Using a medium saucepan, add the butter, chocolate and 2 cups of chocolate chips. Place over medium-low heat, stirring often, until butter and chocolate have fully melted; set pan aside to cool.

Using a medium bowl, mix together the eggs, sugar and vanilla; stir the egg mixture into the warm chocolate mixture.

Using another medium bowl, sift together the flour, baking powder and salt; stir the flour mixture into the chocolate mixture.

Stir the remaining 1½ cups of chocolate chips into the batter.

Divide batter evenly between 2 baking pans. Bake at 350°F for 30-32 minutes, or until a toothpick inserted into the brownies comes out mostly clean.

Let brownies cool in pans for 15 minutes and then transfer to cooling racks until completely cooled.

Using a countertop mixer, cream together butter, brown sugar and granulated sugar until light and fluffy (~3-4 minutes on medium speed).

Add peanut butter; mix until well combined.

Add flour ½ cup at a time, mixing after each addition until well combined.

Add milk; mix until well combined.

Add chocolate chips; mix until well combined. Set cookie dough aside.

Heat about 1" of water in a medium saucepan until it begins to simmer slightly. Place a small, heat-proof bowl over the saucepan. Add all of the ingredients (chocolate, butter, corn syrup and water) to the bowl, and stir occasionally until the chocolate has melted and the mixture is smooth.

Remove mixture from heat and allow it to cool at room temperature for 20 minutes before pouring over cake.

Using a countertop mixer, cream the butter on medium speed for 2-3 minutes.

Reduce speed to low and add the powdered sugar 1 cup at a time, mixing after each addition.

Add milk, vanilla and peanut butter; beat on medium-high speed for 3 minutes, or until frosting is light and fluffy.

Line 1 of the cake pans with an oversized piece of parchment paper. Press cookie dough evenly into pan.

Once the brownies have cooled completely, place one layer of brownies on a large cutting board.

Spread 2-3 Tbsp of the glaze evenly on top of the brownies.

Remove cookie dough from pan and place on top of the brownies. Spread another 2-3 Tbsp of glaze on top of cookie dough. Place remaining brownie layer on top.

Cut into 24 slices (6 rows by 4 rows).

Line a rimmed baking sheet with parchment paper and then set a cooling rack on top of pan.

Working in batches, place several brownie squares on the cooling rack. Drizzle spoonful of glaze on top of each brownie. Let glaze cool and harden slightly.

Using a piping bag fitted with a large star tip, pipe dollop of frosting in the center of each brownie.