Doubt they use grass fed butter, but I love the baklava at Papa Cristo's at Pico and Normandie. Second for me would be Baklava Factory in Glendale, Encino and North Hollywood.
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Papa Cristos
2771 W Pico Blvd, Los Angeles, CA 90006
Pico Cafe
8944 W Pico Blvd, Los Angeles, CA 90035