Prepare Pistachio Cream: Blend pistachios until a fine paste forms, about 2-3 minutes. Melt white chocolate and neutral oil; mix into the pistachio paste until smooth. Add confectioners' sugar to taste.

Make Coffee Soak: Combine cooled coffee, granulated sugar, and vanilla extract in a bowl. Stir until sugar is dissolved, about 1-2 minutes.

Combine Mascarpone Mixture: Whisk mascarpone cheese, confectioners' sugar, and vanilla extract until smooth. In a separate bowl, whip heavy cream to stiff peaks and fold into mascarpone mixture.

Layer Dessert: Dip each ladyfinger into the coffee soak quickly, then arrange them in a 9x13 dish. Spread half the mascarpone mixture over the ladyfingers, followed by a layer of pistachio cream.

Repeat Layers: Add another layer of dipped ladyfingers, remaining mascarpone filling, and finish with pistachio cream. Smooth the top with a spatula.

Chill: Cover and refrigerate for at least 6 hours or overnight for best flavor melding.

Prepare Topping: Whip additional heavy cream with confectioners' sugar, cornstarch, and vanilla extract until stiff peaks form. Pipe or spread over the tiramisu.

Garnish and Serve: Drizzle remaining pistachio cream over the topping and sprinkle with chopped pistachios. Slice and serve.