The dough:
Work as quickly as possible to prevent the dough from becoming warm.
Don’t skip the chilling time. Chilling prevents the cookies from spreading out too quickly once they're in the oven.
The filling:
The filling should be thick enough to prevent the cookies from collapsing and losing their shape during baking. If you are filling your Hamantaschen with jam or jelly, you can make them a little thicker by mixing them with cookie crumbs (like graham crackers), cake crumbs (from a stale leftover cake), or chopped nuts. It will prevent them from spilling out during baking.
Don’t put in too much filling, or you won’t be able to close the Hamantaschen. One teaspoon is enough.
Baking:
The cookies should remain relatively white and not brown.
The cookies will start changing color on the bottom when ready to take out of the oven. If you want them extra crunchy go ahead and give them a few more minutes.