Pure almond meal shortbread

I am trying to bake some shortbread with almond meal alone. This is what I've got:

Recipe: Pure almond meal shortbread

Ingredients:
- 1 cup almond meal
- 4 TB butter
- 2 TB cornstarch
- 1/2 tp salt
- 2+1/2 TB white sugar
- raw almonds, soaked and sliced for topping

Procedure:
1. Mix almond meal with cornstarch and salt in a medium bowl.
2. Chop butter into small pieces. Use a fork to flake the butter until it forms a smooth paste.
3. Add the softened butter by spoonful into the flour mixture and use hand to mix them together until they are just incorporated to form one ball of dough.
4. Make small 1" balls out of the dough. Press each down into a mini-tart mold.
5. Place a slice of soaked almond on each piece of dough, pressing it down.
6. Preheat oven to 300F. Place the tart tray in the oven and bake at 300F (or slightly lower temperature such as 275F) for 20-25 minutes, until the top is lightly brown.

Results:

4:23pm, shortbread dough ready to bake:

4:54pm, shortbread baked 30 minutes:

4:55pm, shortbread collapsed tops:

4:58pm, shortbread fallen apart when turning out of the pan:

Observations:

1. In this time, the butter and the almond meal dough blend so well that I could knead the dough rigorously. The final dough is very moist and pliable.
2. The greatest surprise comes when after baking for 30 minutes, the puffy shortbread collapses! I think that's because almond meal has no gluten at all. Somehow, it just doesn't hold the puff while baking.
3. This shortbread has a pure taste of almond because no substantial amount of flour is present.
4. After the shortbread has been kept at 150F for a few hours, they harden, but remain chewy.

Remarks:
I've just found out that to make hard cookies, the important thing is to minimize kneading the dough. This can prevent air bubbles from being trapped in the dough. The puff of the cookies during baking comes from such air bubbles. So, the dough should be just incorporated, with minimal handling, if hard cookies are desired.