Why did my thumbprints crack?
Usually the dough is a little dry or too cold when you press. Let the dough sit at room temp for 5 minutes, then press again gently. Also make sure you measured flour correctly. Spoon and level it, do not pack it.
Can I fill them before baking?
You can, but I do not recommend it for this soft style. Filling after the first bake keeps the jam brighter and helps it stay in a neat pool instead of melting outward or soaking in.
What jam works best?
Thicker jams and preserves are easiest: raspberry, strawberry, apricot, cherry. If yours is runny, you can stir in 1 teaspoon chia seeds and let it sit 10 minutes (this can help it gel, and you will see the seeds). Or simmer the jam for a couple minutes to thicken, then cool completely. If your preserves are super chunky, give them a quick stir or mash so they spoon neatly into the wells.
Can I use something besides jam?
Yes. Nutella, dulce de leche, lemon curd, or thick chocolate ganache all work. Add them after the first bake, just like jam.
How do I keep the centers from puffing up?
Make a deep enough well and re-press if needed right when they come out of the first bake. Use the back of a teaspoon if you want super neat wells.
Do I have to roll them in sugar?
Nope. It adds a crisp edge and a little sparkle, but you can skip it if you prefer a less-sweet cookie. The dough still bakes up nicely.
Can I use salted butter?
Yes. Use salted butter and reduce the added salt to 1/4 teaspoon.