¼ cup raw pistachios
1½ cups chilled heavy cream
½ tsp. vanilla extract
Pinch of kosher salt
1 tsp. powdered sugar
⅔ cup raspberry jam or preserves
36 Biscoff cookies
½ pint pistachio ice cream, softened at room temperature until pliable
Line a 9x5" loaf pan with plastic wrap, leaving a few inches of overhang on all sides. Chill pan until ready to use. Toast nuts in a dry small skillet over medium heat, tossing occasionally, until golden brown, 5–8 minutes. Let cool, then coarsely chop; set aside.
Using an electric mixer on medium-high speed, beat cream and powdered sugar in a large bowl until stiff peaks form, about 3 minutes. Place jam in a medium bowl and whisk to loosen, then gently mix in half of whipped cream. Mix vanilla and salt into plain whipped cream.
Scoop half of vanilla whipped cream into prepared loaf pan and spread into an even layer. Arrange a layer of cookies on top, breaking or cutting to fit as needed. Add half of raspberry whipped cream, smooth into an even layer, and top with another layer of cookies. Dollop ice cream across top and smooth into an even layer. Add a third layer of cookies, followed by remaining raspberry whipped cream. Repeat with a fourth layer of cookies and finally spread remaining vanilla whipped cream over (don’t worry if it’s a little higher than edges of pan). Scatter reserved pistachios on top. Cover with plastic overhang and freeze until set, at least 6 hours.
To serve, using plastic overhang, unmold cake (if it’s hesitant to come out, run the sides of the pan under warm water for a few seconds to loosen) and cut into slices.