last week

[Lone]

I was very puzzled to find the following sentence in a business writing magazine:

"Further to our conversation of last week, I would like to ..."

The writer of the article specifies that the preposition "of" should be placed before "last week".

This contradicts my understanding. What I learned was prepositions were not required before time expressions like "last week". So, is the above sentence incorrect? Should it be "Further to our conversation last week" (without "of") instead?

Thank you very much!

[Josef Essberger]

It’s slightly old-fashioned or perhaps legalese but perfectly correct in a formal setting, as is your other option in a less formal setting