Katmaan, here's the lowdown on the chocolate pie at Lawrence's:
Lawrence's Sandwich Shop was sold shortly after Mr. Lawrence died in 1980. Linda G. bought it, named it Linda's Sandwich Shop, and ran it until October 2003. Beth Hanna, a former food writer from the local daily, now owns and operates the shop.
It took some time to track Linda down as she's retired and lives outside Lexington. I phoned long distance and had a very nice talk with her about the restaurant and the chocolate pie you so loved in the early 70s.
Linda doesn't think there was ever a homemade recipe for that chocolate pie. When she bought the restaurant from the heirs, she discovered a huge supply of instant chocolate pudding mix, which she immediately threw away. At the time she believed the mix was the filling for Mr. Lawrence's chocolate pies. She continues to think so.
During her years operating the shop, Linda served a homemade chocolate pie, using her own recipe. Though I lived directely across the street from Lawrence's in 1974 and lunched there frequently, I cannot remember having the chocolate pie.
I wish I could have given you a wonderful recipe. The good news is that this particular instant pudding (and pie filling) is probably still around. I wish I had asked Linda if she remembers a brand name (it could have been a common supermarket brand, or a institutional mix from a food broker). If you need to know, contact me. If you would like to talk directly with Linda, I'll ask her permission to share the phone number with you.