Sunken Moon Cakes

I made moon cakes for the first time at the weekend, but rather than the glazed apearance and firm texture they usually have, they sunk in the middle. Without building the dough equivalent of the great wall of china to help keep the filling in, is there another way I can 'reinforce' the walls to stop them sinking?

I used this recipe:

• 300g Low Protein flour
• 250g Golden syrup
• 70g Peanut oil
• 1/2tsp Alkaline water
• 1/8 Lemon juice from a whole lemon
• Lotus paste
• Pandan paste
• Steamed Salted Egg Yolk (Steamed 10 mins under high heat)

Egg wash - 2 egg yolk plus 1 whole egg (lightly beaten)

Method

1. Mix syrup, peanut oil and Alkaline water and lemon juice together, stir it well.
2. Slowly pour the sifted flour and knead into a fine dough.
3. Cover and rest it for 4-6 hours in the fridge. Better if you rest it overnight.
4. Mix the melon seed with the lotus paste. Weight the lotus paste 110g each and roll into a round ball.
5. If you intend to add 1 salted egg yolk, reduce the lotus paste to 80g each and wrapped the egg yolk in it.
6. Weight dough 55g each and roll into a ball.
7. Flatten the dough ball and place a lotus paste ball on top, wrap with it.
8. Dush some flour on the mooncake mould, knock out excess flour.
9. Place mooncake inside the mould, flatten dough to conform to shape of mould.
10. Knock the mooncake mould on solid surface and slowly remove the mooncake and place on a baking pan.
11. I apply egg wash twice on the moon cake, hence apply egg wash then bake it at pre-heated oven at 180c for 11 minutes.
12. Remove mooncake from oven and set aside to cool for at least 15mins.
13. Apply egg wash again and bake at preheated oven at 180c for 11mins.
14. Remove mooncake from oven, immediately transfer to wire rack to cool. Keep in air tight container and allow it to set. Serve after 1-2 days after the colour is uniform and the skin is soften and moist.