• Preheat oven to 350°F.

Crust

• In a medium bowl, combine the Oreo cookie crumbs with the melted butter, mixing well with a fork. (You want every crumb coated in the butter as this will be the glue that holds it together.)
• Pour the coated Oreo crumbs into an 8-inch pie dish. Pat them flat with your hand and then use a kitchen glass to press flatter. Start at the center and work out and up the sides. Set aside.

Brownies

• To a large bowl, add cocoa powder, flour, baking powder, salt, and espresso powder. Whisk to combine. Set aside.
• To a large saucepan over medium heat, add butter and sugar. Once the butter has melted, bring it to a low boil and cook for 2 more minutes, stirring occasionally or until it reaches 230°F on an instant-read thermometer.
• Remove from heat and stir in the chocolate chips and vanilla until completely melted. (The mixture may still be grainy.) Let cool for about 10 minutes.
• When ready, add eggs, one at a time, stirring constantly until smooth.
• To the flour mixture, add the chocolate mixture. Mix until JUST combined. The batter will be very thick.
• Spread the batter into the prepared pie crust and bake for 30-35 minutes, or until slightly puffed. Set aside to cool completely.

Homemade Whipped Topping

• Add heavy cream to a mixing bowl. Start mixing at the lowest speed, and then gradually increase speed to medium until the cream starts to get thicker. (The gradual progression prevents you from spraying yourself with cream.)
• When the cream starts to thicken, stop the mixer. Slowly add in the confectioners' sugar and then resume mixing again, starting with low speed and increasing to medium speed, and eventually moving to a high speed.
• The cream will thicken and start to peak. Mix on high until the cream is thick and stiff. This happens quickly, the stage between soft and stiff peaks, so watch it closely.
• Store the whipped topping in the refrigerator for up to 10 hours if not using right away.
• Top the brownies with the whipped topping and drizzle with chocolate syrup (optional) before cutting and serving.