In a large mixing bowl, whisk the double cream with the icing sugar until soft peaks form. Be careful not to over-whip—you want the cream fluffy but not stiff.

Fold in the mascarpone and pistachio paste until just combined. Don’t overmix; the goal is a smooth, creamy filling with the perfect pistachio flavor.

Pour the coffee into a shallow dish. Quickly dip each sponge finger into the coffee for a couple of seconds on each side—enough to soak up the flavor without making them soggy. Arrange them in an even layer across the base of your dish (about 9x13 inches works perfectly).

Spread a generous layer of pistachio cream over the soaked sponge fingers. Repeat with another layer of coffee-dipped fingers, then another layer of pistachio cream. Continue until all the sponge fingers are used, finishing with a final layer of pistachio cream.

Spoon some pistachio paste into a piping or sandwich bag, snip off the tip, and pipe thin lines across the surface. Use a toothpick to drag through the lines in the opposite direction, creating a feathered pattern.

Cover the dish with cling film and refrigerate for at least 6 hours—ideally overnight. The longer it chills, the more the flavors meld together.

Remove from the fridge about 20 minutes before serving. Sprinkle chopped pistachios on top for texture and color. Slice into portions and enjoy!