I wanted the same red heart effect (the cookies were for a Valentine's Day event) but an issue presented itself: should the jam go in before the cookies are baked or after? Similar recipes I have used in the past, as well as many commenters on allrecipes.com recommended that the jam be placed in the thumbprint before, as this enhanced the taste. However, both PB&J recipes called for the jam after baking.
Since the cookies weren't for my private enjoyment, I wanted a) yummy, and b) presentable result. Therefore, I conducted a test! I rolled 4 cookies, made a thumbprint in 2 of them, a heart print (using my index finger) in 1 of them, and shaped the last one into a heart with a thumbprint. I filled all with jam but one of the balls.
After baking, I found that:
- the heart-shaped cookie lost its shape
- the heart print cookie turned into a triangle print cookie
- the cookies with jam developed unsightly light pink rings around the jam centres (due to cookie spread)
- the cookie without jam lost the thumbprint almost entirely (due to cookie spread)
- the pre-bake jam-filled cookies held a lot less jam than the post-bake jam-filled cookie
Clockwise from top: heart print cookie, heart shaped cookie, pre-bake jam-filled round, post-bake jam-filled round.
Since the pre-bake jam-filled cookies looked a little silly, I opted for filling my batch with jam after baking. I made thumb prints and heart prints in the cookies before baking, but due to spread, I had press down the prints again after baking. Filling in the jam after baking also makes transportation easier - if you're willing to cart around a jar of jam!
I couldn't manage to take a photo of the jam-filled cookies because they were all eaten! Overall, very tasty!