Prune filling, a widely popular filling for these triangular cookies, became traditional in 1731. David Brandeis, a plum preserve merchant, was acquitted after being charged with poisoning some plum preserves. He was released from prison just before Purim. In order to celebrate his freedom, the townspeople of Jungbunzlau in northeastern Bohemia (now part of the Czech Republic) filled the hamantaschen with povidl, plum preserves, and referred to the holiday as Povidl Purim.
- Combine the prunes, sugar, lemon juice, lemon zest, cinnamon, and vanilla in a processor work bowl. Process the mixture until smooth.
- Transfer the mixture to a bowl and fold in the finely chopped walnuts. Cover and refigerate until ready to use.