Stir together the cookie crumbs and melted butter, then firmly press the mixture across the base and slightly up the sides of the pan. assemble

Whisk the flour, cocoa powder, baking powder, and salt together in a bowl and reserve for later. mix

In a separate large bowl, blend the oil, melted butter, sugar, and vanilla until smooth, then mix in the eggs until fully incorporated. mix

Fold the dry mixture into the wet ingredients just until combined, avoiding overmixing. mix

Spread the brownie batter evenly over the prepared crust. assemble

Place the pan on a larger baking tray and bake until the center tests with moist crumbs, then remove from the oven to cool slightly. bake

Whisk the egg yolks in a bowl until smooth and set aside. prep

Combine sugar and cornstarch in a saucepan, whisking until lump-free, then stir in the milk. mix

Cook the mixture over medium heat, whisking constantly until it begins to gently simmer. cook

Slowly whisk hot milk into the egg yolks to temper them, then return everything to the saucepan. mix

Continue whisking as the custard thickens and boils briefly, then remove from heat and stir in butter, chocolate, and vanilla until smooth. cook

Pour the pudding over the brownie layer, smooth the surface, cover directly with plastic wrap, and chill until fully set. assemble

Whip the cream with powdered sugar and vanilla until stiff peaks form. mix

Remove the chilled pie from the pan, transfer if desired, and spread the whipped cream evenly over the top. finish

Decorate with chocolate curls or cocoa if desired, then refrigerate until ready to serve. finish