Can I Help to Cheer You? - S6-E18
Continuity mistake: When Tommy is saying to Eric "We've been hanging out with each other for a long time now," Eric's coffee mug is mere inches from his face. When the shot changes, the mug is almost set down on the table. (00:00:58)
Answer: Topanga's middle name is never specified. Considering her sister's name is Nebula Stop-the-war Lawrence, Topanga's is probably something equally unusual.