Prepare the pan: Line the bottom of a 10-inch springform pan with parchment paper. Lightly grease the sides or line them with acetate cake film if desired.
Make the cookie crust: Place the crushed cookies in a large mixing bowl. Add the melted butter and mix until the crumbs are evenly moistened and resemble wet sand. Add the milk one tablespoon at a time, using only enough for the mixture to hold together when pressed.
Form the crust: Transfer the cookie mixture to the prepared pan. Spread it evenly across the bottom and press it down firmly using the back of a spoon or the bottom of a glass. Refrigerate the crust while preparing the cherry layer.
Cook the cherries: Place the pitted cherries and sugar in a medium saucepan. Cook over medium heat for 5–7 minutes, stirring occasionally, until the cherries soften and release their juices.
Thicken the cherry cream: Mix the cornstarch and cold water in a small bowl until completely smooth. Slowly pour the slurry into the simmering cherries while stirring constantly. Cook for another 1–2 minutes, or until the mixture thickens.
Add the cherry layer: Remove the cherry mixture from the heat and let it cool for 5–10 minutes so it is no longer piping hot. Spread it evenly over the chilled cookie crust. Allow the cherry layer to cool completely before adding the pistachio cream.
Prepare the vanilla cream: Add the cold milk, instant vanilla cream powder, sugar, and vanilla sugar or extract to a large mixing bowl. Beat with an electric mixer according to the cream powder package directions, or until thick, smooth, and creamy.
Add the pistachio flavor: Add the pistachio cream and heavy cream to the vanilla mixture. Beat briefly until the cream is smooth and evenly combined.
Add the pistachio layer: Spoon the vanilla pistachio cream over the completely cooled cherry layer. Spread it evenly and smooth the surface with an offset spatula. Return the cake to the refrigerator.
Prepare the ganache: Place the chopped white chocolate in a heatproof bowl. Heat the heavy cream in a small saucepan until steaming but not boiling. Pour it over the chocolate and let it stand for 2 minutes.
Finish the ganache: Stir the white chocolate and cream until completely smooth. Add the pistachio cream and stir until evenly combined. Let the ganache cool for several minutes until it is still pourable but no longer hot.
Decorate the cake: Pour the ganache over the pistachio cream layer and spread it evenly. Decorate the top or edges with chopped pistachios.
Chill: Cover the cake and refrigerate it for at least 4 hours. For the cleanest slices and best texture, chill it overnight.
Slice and serve: Carefully remove the springform ring. For clean slices, dip a sharp knife in hot water and wipe it dry before every cut. Keep the cake refrigerated until serving.
