Chill a large mixing bowl and whisk in the refrigerator for about 10 minutes. Then, add double cream and icing sugar, whipping until soft peaks form, about 3-5 minutes.

In a separate bowl, combine mascarpone and pistachio cream, gently mixing until smooth. Fold in the whipped cream from Step 1, being careful to maintain airiness.

Brew strong coffee or espresso and let it cool. Pour the coffee into a shallow dish. Briefly dip savoiardi sponge fingers into the coffee and layer them at the bottom of a dish.

Spread a layer of the pistachio cream mixture over the soaked sponge fingers. Repeat with more soaked fingers and cream until all are used, finishing with a creamy layer.

Decorate with a piping bag filled with pistachio cream and swirl with a toothpick to create a feathered pattern.

Cover with plastic wrap and refrigerate for at least 4 hours, or overnight. Before serving, let it rest at room temperature for 20 minutes.