Preheat your oven to 350°F (175°C) and grease a 9x13 inch baking pan.

In a medium bowl, whisk together the dry ingredients: flour, cocoa powder, baking powder, and salt.

In another bowl, mix melted butter with sugar, eggs, and vanilla until smooth.

Gradually add the dry mixture to the wet ingredients until just combined, then pour into the prepared pan.

Bake for 20-25 minutes until the edges pull away slightly and a toothpick inserted in the center comes out clean. Let cool completely.

In a large mixing bowl, beat the cream cheese and powdered sugar with a hand mixer until smooth and creamy, about 2-3 minutes.

Slowly incorporate the whipping cream and a splash of vanilla, mixing until fully combined.

Gently fold in crushed Oreo cookies, ensuring they're evenly distributed.

In a microwave-safe bowl, heat the chocolate chips in 30-second intervals, stirring until melted.

Gradually whisk in the heavy whipping cream until fully combined, creating a silky ganache.

In a clean bowl, pour in the heavy whipping cream and sprinkle in the powdered sugar. Whip until stiff peaks form, approximately 4-5 minutes.

In a trifle dish, layer half of the cooled brownie pieces, followed by half of the Oreo cheesecake filling. Add half of the crushed Oreos, and drizzle half of the chocolate ganache. Repeat the process with remaining ingredients.

Cover the assembled trifle and refrigerate for at least 4 hours, or overnight. Serve chilled.