Preheat oven to 350 degrees. Grease and flour a 9"x13" baking pan. Set aside.

In a large bowl, combine cocoa powder and boiling water. Whisk until well combined.

Add the unsweetened chocolate and stir until chocolate is fully melted.

Stir in the butter and oil, and mix until combined.

Add eggs, yolks, and vanilla. Stir until well combined.

Next, add the sugar and stir until combined.

Add flour and salt, and gently stir until well combined.

Finally, fold in the pieces of bittersweet chocolate.

Pour batter into greased pan and bake at 350 for 30-35 minutes, or until toothpick inserted into center comes out clean.

Cool for 2 hours on a wire rack before cutting.

Combine all ingredients in a medium bowl and stir until well mixed.

Pour mixture into an ice cream maker and freeze according to the manufacturer's directions.

Using a sharp knife, cut about 20-25 1-inch square Gooey Brownie pieces. Set aside.

Scoop Peanut Butter Ice Cream into blender and add 1/2 cup milk.

Blend until you reach desired consistency, adding more milk as needed.

Pour milkshake into glasses, adding brownie chunks as you pour.

Top with whipped cream (optional).