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September Baking Club update

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Why did my cookies turn green?

For September, our baking club challenge was to include at least one vegetable in our baking. And there wasn’t a single carrot cake in sight!

We had a good mixture of savoury and sweet dishes, including a chocolate cake made with kidney beans, a delicious chocolate cupcake with hidden vegetables (I’d never have guessed I was eating broccoli!), a Sally Lunn made with potatoes, a mushroom and onion tart, and a parsnip loaf among others.

I had some HUGE kumara to use, so I searched for recipes to use them in. I’ve made bread rolls with orange kumara before, but the result wasn’t brilliant. I ended up adapting an American recipe for “Sweet Potato Cookies.”

I got a shock on Tuesday morning when I uncovered the mixture that had been in the fridge overnight. It had turned green! It looked awful, like a mould had grown along all the ridges of the biscuit dough. It smelled and tasted fine, so I went ahead and rolled it into biscuits. The baking turned them a wonderful golden brown colour, though they still had a slight greenish tinge in the middle. It turns out that kumara and other sweet potatoes, especially the purple variety, often turn green when cooked and then left exposed to air. It’s an oxidation process involving the soluble pigments that I don’t fully understand. However, it’s perfectly safe to eat and doesn’t affect the smell or taste. I’m glad I didn’t halve the recipe as I had originally planned – these went down a treat at baking club and among library staff.

green cookies Copy

Emma’s Kumara Cookies (adapted from The Novice Chef’s Sweet Potato Cookies).


  • 1 large   kumara
  • 1 tsp      honey
  • 3 C          flour
  • 1 Tbsp   cornflour
  • 1 tsp      baking powder
  • 1 tsp      baking soda
  • ¾ tsp     ground cinnamon
  • ½ tsp     ground nutmeg
  • 200g       butter, melted
  • ¾ C         sugar
  • 1 large   egg
  • 2 tsp      vanilla essence


  1. Peel your kumara – the huge ones we’ve been getting this winter are more than big enough, or you might need a couple of regular-sized ones. Chop into small pieces – the smaller the pieces, the faster they will cook. Put into a pot and cover with water. Boil until soft. Drain the kumara and mash with a heaped teaspoon of honey. You need one cup of mashed kumara for this recipe. The remainder freezes well and is delicious spread on toast or cruskits!
  2. While you wait for your kumara to cook, combine flour, cornflour, baking powder, baking soda, cinnamon and nutmeg. I think ginger would also work well, or mixed spice. Set aside.
  3. Use a beater or mixer to combine the mashed kumara, melted butter and sugar.
  4. Mix in egg and sugar.
  5. Mix in flour mixture until combined.
  6. Cover and refrigerate for one hour or overnight.
  7. Preheat oven to 180°C.
  8. Roll into flattened balls and place on two baking trays lined with baking paper. You will get about 36-40 cookies.
  9. Bake for 18 minutes or until tops are set. Transfer to wire racks to cool.

Next month’s theme is “bake from a library book” – we are well stocked at all three libraries, so have a go at home. The library baking club meets on the first Tuesday of every month at 10:30am at Hastings War Memorial Library. 

15 September 2022

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