The instructions state to add vanilla extract but it is not in the list of ingredients. How much vanilla?

Erin's pretty good about responding to questions about her recipes however it is St. Valentine's Day and as a professional baker she may be busy with other responsibilities/commitments today.

I suggest you wait for her response if possible.

If you need to make this right now, I would probably use 1/4 teaspoon of vanilla extract, maybe as much as 1/2 teaspoon (after tasting the batter), but no more.

Best of luck.