Ultra Violet

Although I don't bake at home very often, I am always on the lookout for new ideas and recipes. I am especially intrigued by recipes that cater to specific dietary restrictions. Having trained in classical French pâtisserie, I have little professional experience with gluten-free, dairy-free and vegan baking. Some techniques are particularly fascinating -such as using aqua faba (chickpea cooking water) instead of egg whites- and others are just plain perplexing. My interest is not entirely self-motivated: food allergies and intolerances are on the rise. In one of my close friend's family alone, there are nut, dairy and stone-fruit allergies as well as a coeliac: baking for a family gathering has become a minefield.



This recipe for a sweet potato and blood orange drizzle cake is both gluten and dairy-free, three words that make some people cringe. Admittedly, attaching those words to a dessert puts me a little out of my comfort zone, but this cake is a revelation. It is moist, has a tender crumb and a lovely crust, yet it contains no flour and a not-excessive amount of sugar, two ingredients that contribute a lot to a cake's texture. Those with egg-free baking experience may want to push the envelope further and make the cake completely vegan, but that would have added too many parameters to my recipe testing. If you are trying to cut back on refined sugar, the drizzle can be left out and you will still have a moreish cake to enjoy with a cup of coffee or tea (or for breakfast!)



I used purple sweet potatoes and blood oranges just for the wow factor, so any sweet potato and citrus combination will do for this cake. In fact, the sweet potato can be substituted with other vegetables: beetroots would result in an equally vibrantly hued cake, but carrots, parsnips and even regular potatoes could work as well. Pumpkin and kabocha squashes are also good substitutes. It might seem like a lot of effort to use cooked sweet potatoes in this recipe, but it is important: the starch needed to give body to the cake is unavailable until the potatoes are cooked.



Can we just take a minute to admire this colour though? Last December, Pantone announced that Ultra Violet purple would be the colour of 2018, and who am I to argue with them? Although I don't outright object to food colour, I do try to minimize my use of it at home, so I always jump at the opportunity to work with whole foods to create vibrant colours. Beetroot is a favourite, but these purple sweet potatoes just might take the cake... Sorry, I just can't resist a bad pun! To help preserve that vibrant colour, only a token amount of baking powder is used in the batter, so it is extremely important to whisk the eggs until the ribbon stage, or tripled in volume, as the eggs are the main source of airiness. Thorough whisking will take at least six minutes with an electric mixer; if you would rather forgo this step, you can increase the baking powder to 1 teaspoon. However, any bright red or purple colour might get muddied by the leavener.



Purple Sweet Potato and Blood Orange Drizzle Cake
Makes two 10x20cm (4"x8") loaves or one 20cm (8") round cake

1 blood orange
150g/1 cup icing sugar
480g/2 cup cooked sweet potato (about 650g/23oz raw, unpeeled)
330g/2 cups cooked quinoa (about 100g/½ cup raw)
5 large eggs
250g/1¼cup maple sugar or light brown sugar
125ml/ ½ cup vegetable oil
1 tsp cream of tartar
½ tsp baking powder
1 tsp vanilla extract
3 scrapes grated tonka bean or nutmeg

Line two loaf tins or a round cake tin with baking parchment.
Pre-heat the oven to 180°C/ 350°F.

Peel the sweet potato, and cut into chunks. Place in a covered bowl, and microwave for 5 minutes on high power, in 90 second increments. Alternatively, cook the sweet potato by boiling or steaming for 15-20 minutes until soft. Drain the sweet potato and keep the cooking water for the quinoa. 
Mash the drained sweet potato: the smoother the mash, the finer the texture of the final cake.
Zest the orange, and mix into the mashed sweet potato, along with the vanilla extract and grated tonka bean or nutmeg.
Bring a large pan of water to the boil, and cook the quinoa until nearly overdone, about 20 minutes. Drain the quinoa, measure out the necessary amount, add two eggs and the oil, and blitz with a blender until smooth. Combine with the mashed sweet potato.
In a clean bowl, combine the remaining eggs, sugar and cream of tartar, and whisk to the ribbon stage, or tripled in volume, about 6-8 minutes.
Incorporate the sweet potato mix into the eggs with the electric mixer on a low speed.
When the batter is thoroughly combined, stir in the baking powder and mix well. 
Divide the batter amongst the cake tins, and bake until the cake is done, about 50-60 minutes for small loaves, or 75 minutes for a larger round cake. 
This cake is too moist for the toothpick test, so it is important to check if it's done by poking the surface: it should feel firm and dry to the touch, but still have some spring
While the cakes are baking, juice the zested blood orange into a saucepan, and stir in the icing sugar.
Bring up to a boil, remove from the heat when the syrup starts to rise. Set aside.
Allow the cakes to cool completely before drizzling the syrup, otherwise it will soak in all the syrup.




Although I mention three cooking methods for the sweet potato, the microwave will yield a drier mash, in a lot less time. If you do not have a microwave oven, try to cook off both the quinoa and the sweet potatoes ahead of time so that they can cool down completely before being mixed into the batter. Cold quinoa is difficult to blitz properly, so if your blender or food processor cannot handle cold quinoa, warm it up before pureeing, then allow to cool down completely. As with most vegetable-based cakes, this sweet potato drizzle cake will keep, unrefrigerated, for several days -if you can keep your hands off of it! Serve it with a dollop of (non-dairy) Greek yoghurt or a scoop of ice cream, and enjoy.





Bon App'!