And the missing number is ?

It's my birthday today. I'm 50 plus a few years.
Last night the chief and I went to Eat on the Green at Udny Green for a birthday meal. For reasons I cannot fathom we've never been there despite lots of good reports. We were not disappointed - a great dinner and fantastic service. We'd a quietist day today but had some more eating and drinking with some family this afternoon. The chief produced this wee cake but could not find a ....7.