Line 7 inch tart pan that has removable bottom with parchment paper. For crust, in food processor, pulse walnuts until finely chopped, almost a flour. Add dates, cardamom, and salt; pulse until a ball forms and mixture is sticky. Firmly press into prepared pan. Clean food processor.

In cleaned food processor, puree cashews until mostly blended. Add remaining filling ingredients and puree until smooth and creamy, 1 to 2 minutes. Smooth onto prepared crust and refrigerate for at least 12 hours.

Before serving, run knife around inner wall of pan and unhinge pan. Slice cake and serve. Store in refrigerator for a few days or freeze for up to 2 months.