Purple Yam Mooncakes

Vegetarian Purple Yam Mooncakes filled with homemade purple yam and sweet potato paste center to simulate salted egg yolk. Melon seeds provide texture.

I know it sounds crazy but I am always on the lookout for purple yam or purple sweet potatoes. It seems these purple tubers are no where to be found in my neck of the woods. That is, until the Sunday before this recently past Mid Autumn Festival. On our way home from the Minnesota Zoo, we stopped by an Asian market, and lo and behold, there they were!

I was ecstatic! (just kidding) My waiting and hoping that someone would sell them are over, at least for now. The price was more than double that of regular sweet potatoes but I wasn’t going to pass it up. I bought two pounds, enough for making these Purple Yam Mooncakes and also Bubur Cha Cha, which I’ll be sharing soon.

The color of these purple yam is not as deep as those found in Malaysia. When cooked and pureed, it is more like a lilac or a pale purple color. Not a brilliant purple but quite pretty, especially when paired with orange sweet potatoes. It did deepen slightly after baking. The flesh is mildly sweet and very smooth, perfect for my purpose of making it into a paste. 🙂

I made these Purple Yam Mooncakes last Wednesday, knowing that both my sons will be home from college on Friday. Since the purple yam paste was quite moist, the crust soften in a day, just in time for the Mid Autumn Festival on Thursday, September 15th. Between the four of us, we had our fill of these tasty treats for tea time over the weekend.

You may or may not see some green tinges along the inside of the crust. If you do, do not be too alarmed. I did see it in the first cake I cut into and was duly concerned. Only one day and my mooncakes have gone bad? I almost threw it away but then I have 5 more untouched, beautiful mooncakes. What should I do?

I remember that purple beans turn into green beans when cooked and so I promptly search the internet for answers. I found them here and here. A few other food bloggers also experienced this when they baked purple sweet potatoes in cakes and bread with baking soda (an alkaline). Apparently, the anthocyanins in these tubers are pH sensitive, appearing blue or purple in the presence of acidity. In this case, it reacted with the alkaline water used in the dough, losing its acidity and turning green in the process. Thankfully, it is just food science!

One way to get around this is to reverse the position of the purple yam paste and the sweet potato paste. If you do that, you will have a purple center instead of an orange center. Imagine a pídàn (皮蛋) or century egg yolk in your mooncake…yikes! Haha! Whatever you decide, I hope you give these Purple Yam Mooncakes a try. They are quite delicious and you can adjust the sweetness to your liking. That said, they are best eaten the day after baking and consumed within 3 days. Make them in small batches and eat them while they are fresh and moist.

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Purple Yam Mooncakes

Prep Time

1 hr

Cook Time

50 mins

Total Time

1 hr 50 mins

 

Vegetarian Purple Yam Mooncakes filled with homemade purple yam and sweet potato paste center to simulate salted egg yolk. Melon seeds provide texture.

(Makes 6 mooncakes)

Course: Cakes, Dessert

Cuisine: Chinese

Servings: 12

Calories: 324 kcal

Author: Linda Ooi

Ingredients

• 2 cups cake flour (270g)
• ½ cup golden syrup (120g)
• 1/3 cup vegetable oil (80ml)
• 1½ tsp alkaline water (7.5ml)
• 1 egg yolk mixed with 1 tbsp water for eggwash
• 2 tbsp mooncake glaze

Filling

• 1 lb purple yam (peeled and cubed) (450g)
• ¼ cup vegetable oil (60ml)
• ¼ cup sugar (55g)
• ½ lb orange sweet potatoes (peeled and cubed) (225g)
• 2 tbsp vegetable oil
• 2 tbsp sugar
• ¼ cup kuachi (melon seeds) (30g)

Instructions

1. You will also need a 150g to 185g mooncake mold.
2. Steam purple yam for 10 minutes until very soft.
   
3. Remove and puree with an immersion blender while still warm. Do the same for sweet potatoes.
   
4. Combine pureed purple yam, ¼ cup (60ml) vegetable oil, and ¼ cup (55g) granulated sugar in a nonstick fry pan. Cook over low heat until sugar has melted and vegetable oil is fully incorporated into the purple yam puree. This should take about 2 to 3 minutes. Do the the same for sweet potatoes but use only 2 tablespoons vegetable oil and 2 tablespoons granulated sugar.
   
5. Toast kuachi (melon seeds) over medium heat for about 2 to 3 minutes. Remove and allow it to cool. Mix into purple yam paste.
6. Divide and form sweet potato paste into 6 balls of 1¼ oz (35g) each. Divide and form purple yam paste into 6 balls measuring approximately 3 oz (85g) each. Wrap each portion of purple yam paste over each portion of sweet potato paste to form 6 balls of filling weighing (4¼ oz) 120g each.
   
7. Combine golden syrup, vegetable oil, and alkaline water in a small bowl or measuring cup.
   
8. Sift cake flour into a large bowl. Make a well in the center. Pour syrup mixture into well and mix with a spatula to form a soft dough. Cover with shrink wrap and let dough rest for 30 minutes.
   
9. Lightly dust work surface with cake flour. Knead dough until smooth adding a little flour if necessary. Divide into 6 portions of 50g each. You will have roughly 100g excess dough.
   
10. Take a portion of the dough and spread it into a circle of about 4 inches (10cm) with your fingers. Alternatively, you can roll it out with a small rolling pin.
    
11. Wrap a ball of filling with the dough. Roll the ball of dough and filling between your palms to smoothen.
    
12. Place into flour dusted mooncake mold. Press to conform to the shape of the mold.
    
13. Place on work surface and carefully press spring stamp down to get a nice pattern on the top. Lift mold and gently release mooncake onto your palm.
    
14. Place on a parchment lined baking tray. Repeat with the remaining dough and filling.
15. Bake in a preheated 375°F (190°C) oven for 10 minutes. Remove from oven and allow mooncakes to cool for 5 minutes. Brush on egg wash and return to oven for another 10 minutes.
    
16. Remove from oven and brush the tops only with mooncake glaze. Allow mooncakes to cool completely.
17. Store in an airtight container for one day before serving.
18. Best consumed within 3 days.

I made 3 smaller mooncakes with the excess dough using homemade Red Bean Paste for the filling. Please go to the end of the recipe for the additional steps needed to make the paste more suitable for mooncakes.