In a coffee or spice grinder, grind pistachios to a fine powder.
In a small bowl, stir together pistachio powder and honey. Add ¼ cup (60 grams) water, 1 tablespoon (15 grams) at a time, until mixture reaches a peanut butter consistency. Store in an airtight container at room temperature until ready to use, up to 1 week.
Recipe by Bake from Scratch at https://bakefromscratch.com/spumoni-cake/