Preheat oven to 350°F (175°C).

In a medium bowl, combine the crushed Oreo cookies with the melted butter. Mix well with a fork until every crumb is coated in butter.

Pour the coated Oreo crumbs into an 8-inch pie dish. Press them flat with your hand, then use the bottom of a glass to press them even flatter and up the sides of the dish. Set aside.

In a large bowl, whisk together the cocoa powder, all-purpose flour, baking powder, kosher salt, and espresso powder. Set aside.

In a large saucepan over medium heat, melt the butter and sugar. Bring to a low boil and cook for 2 minutes, stirring occasionally, until it reaches 230°F (110°C) on an instant-read thermometer.

Remove from heat and stir in the chocolate chips and vanilla extract until completely melted. The mixture may still be slightly grainy. Let cool for about 10 minutes.

When the chocolate mixture has cooled slightly, add the eggs one at a time, stirring constantly until smooth after each addition.

Pour the chocolate mixture into the dry ingredients and mix until just combined. The batter will be very thick.

Spread the batter evenly into the prepared pie crust. Bake for 30-35 minutes, or until slightly puffed. Remove from oven and let cool completely.

In a mixing bowl, add the heavy whipping cream. Start mixing at the lowest speed, gradually increasing to medium speed until the cream begins to thicken.

Once the cream starts to thicken, stop the mixer. Slowly add the confectioners' sugar and resume mixing, starting on low speed and gradually increasing to medium-high speed until stiff peaks form.

Store the whipped topping in the refrigerator if not using immediately. It can be stored for up to 10 hours.

Top the cooled brownie pie with the homemade whipped topping. Drizzle with chocolate syrup, if desired.

Cut into wedges and serve.