Made these for cookie trays for a lunch after a memorial service.
I tried a test batch with a Joy of Cooking recipe and they were good, but I noticed a lot of the recipes on line were different and used no leavening agent. So I tried the Joy of Baking recipe. These were so flaky and rich tasting.
I'm not sure how the cookies keep from being too dense with no baking powder or baking soda. Perhaps the air beaten in during the creaming of the sugar and butter and then during the addition of the egg yolk makes them light?
Instead of jam, I used fruit fillings made from dried apricots and dried tart cherries. They have an intense flavor and they don't bubble up and overflow like jam sometimes does.
The other cookies were peanut butter, chocolate chip and a simple crisp lemon cookie. These brought the cookie trays up a notch.
Here is a link that might be useful: Joy of Baking Thumbprint cookie recipes