Prepare Craquelin: In a mixing bowl, cream together softened unsalted butter and granulated sugar until fluffy. Gradually mix in all-purpose flour and cocoa powder until combined. Roll into a thin sheet, wrap in plastic, and freeze for at least 30 minutes.

Make Choux Pastry: In a saucepan, combine water, butter, sugar, and salt. Bring to a boil. Remove from heat and mix in sifted flour. Return to low heat, stirring for 2-3 minutes until dough pulls away.

Add Eggs: Let the dough cool slightly, then beat in eggs one at a time until the mixture is shiny and smooth.

Pipe Choux: Transfer choux pastry to a piping bag. Pipe mounds on a lined baking sheet. Cut the chilled craquelin into circles and place on top of each mound.

Bake: Preheat oven to 400°F. Bake for 15 minutes, then reduce the temperature to 350°F and bake for an additional 20-25 minutes until golden brown.

Cool: Prop the oven door open and cool the puffs inside for 10 minutes, then transfer to a wire rack to cool completely.

Whip Cream: In a chilled bowl, whip heavy cream with powdered sugar and vanilla until stiff peaks form. Fold in crushed cookies.

Fill Puffs: Once cooled, slice the tops of each puff and fill with Oreo whipped cream. Serve immediately.