All butter mince pies are not all butter

Gareth has sent in a festive question to The Engine Room:

I've just bought some 'all butter mince pies' which are very tasty but clearly not all butter. If they were all butter, they'd be a block of butter. What does this mean exactly?

I have it on good authority that it means the mince pies are made with 'all-butter' pastry (the hyphen seems to be optional). This is still confusing because butter is not the only ingredient in all-butter pastry; however, it is the only fat.

In other words, Gareth, your pie pastry doesn't include any other fats, such as margarine.

Back in 2007, when The Engine Room was only a few months old, I blogged about all-butter cookies. As that was the first post on this blog to include a picture, it's only fitting that I should share with you now an image of delicious all butter mince pies: