The One Where Ross Got High - S6-E9
Corrected entry: Rachel claims to be making an "Old-English Trifle" using an "Old-English Cookery Book." When she describes the ingredients she says "Beef sauteed with peas and onions." Then Ross looks at the book and realises that the pages are stuck together exclaiming "She's made half an Old-English trifle, and half a shepherds pie." The problem here is that a shepherds pie is made with lamb; a cottage pie is made with beef. Therefore, not only is this simply wrong, but it also shows they are not using an English cook book as it would never make such a basic mistake as this.
Correction: The book is never said to be an "Old-English Cookery Book". In fact when you look closely you will see that it is some kind of magazine called something like "Cooking skills". The only English thing mentioned is an "English Trifle".