"I've been looking for the perfect thumbprint cookie recipe and the search is over....this is it. I would suggest start checking the cookies at 15 minutes, I took mine out at 16 minutes and they were perfect. After the first trial batch I made another, substituting orange for the lemon and melted chocolate for the jam. But I think the best was the final batch, I didn't use any citrus and filled each indentation with ground almonds and caramel, topped each with a small sprinkle of coarse sea salt while warm. This is the beauty of a good thumbprint recipe, you can fill it with anything that you like.