I used to know someone who was born in the 1910s and raised in Budapest, who made a filling for blintzes out of jam and ground walnuts.
I now know someone (unrelated to the first person) who was born in the 1920s and raised in Arad speaking Hungarian, who makes a filling for baked goods out of jam and ground walnuts.
So I guess that filling is an Hungarian specialty. What's it called in Hungarian? Google isn't helping, and the Arad person doesn't recall.