Red velvet variation #11, I think (I for one am amazed that the number is not close to 11 million, but apparently I have not been as industrious as I had previously thought or assumed). So, sweet potato and red velvet. Sounds like a match made in some sort of southern state in some sort of set of united states. And like the rest of the vegetable/cake chimaeras I have attempted, this turned out pretty well. Well done, Team Vegetable.
Red velvet is arguably quite a good candidate for including sweet potato in, since vanilla and sweet potato apparently go quite well together (I also read somewhere that regular potato goes well with vanilla, so don’t hold back from adding a tiny bit to your next batch of mashed potatoes… I will if I ever remember).
As for the sweet potato + white chocolate + ginger combination for the truffles, that’s one of my first experiments using flavour pairing (or… trioing, as the case may be) based on odorant compounds, courtesy of the database at the fantastic FoodPairing site. Sweet potato, white chocolate and ginger share a lot of common odor compounds, which suggests they should complement each other rather well. Only problem is, at the moment the relationships in the database are based on the number of shared odor compounds between two ingredients, not the relative contribution of each odor compound. Maybe they share a heap of odor compounds that play only minor roles in the perceived tastes? (Although the database does only take into account odors that are above the threshold of perception, so presumably there aren’t entirely negligible odors being factored into the flavour relationships).
Strangely enough I’m reasonably sure I don’t have the facilities to conduct gas chromatography to find out the details myself about relative contributions. But until we have a database that shows the relative contributions of individual odorants to overall taste, and can match flavours based on such contributions, I’m going to have to work with numbers for now as a general guide. It’s working pretty well so far!
Ultra-important lesson I learned from devising this recipe: the majority of the flavour of the baked sweet potato is in its skin. Precious, precious, burny-baked skin. I was adding dangerous levels of mashed sweet potato to the cake mix and getting barely any sweet potato taste. But include that skin and you’ve got all the sweet potato flavour you ever dared to hope to wish for.
These cakes were for Dr Tash PhD’s party, which was a cornucopia of fantastic southern-US dishes. The side-dish of sweet potato bake was at least a million percent sweeter than these cupcakes, since these cupcakes don’t involve tooth-achingly and deliciously large amounts of condensed milk and brown sugar. And more’s the pity, really. (Condensed milk icing in the future, yes?)
Sweet potato red velvet cakes
1 medium sized sweet potato
1-2 tbs milk
150g butter, softened
3 large eggs
1 tsp vanilla paste
1/4 tsp salt
380g plain flour
1 tbs cocoa powder
1 1/2 tsp baking powder
1 cup buttermilk
1 tsp bicarbonate of soda (baking soda)
1 tbs white vinegar
Heat the oven to 220°C. Wash the sweet potato, put it on a baking tray and brush it with olive oil. Bake for about 45 minutes, until it feels soft when you insert a sharp knife into it. Leave it to cool a bit so it can be handled. Cut it into a few pieces (leaving the skin on) and process in a blender or food processor until smooth, adding a tablespoon or two of milk to make it easier to blend.
Cream the butter, sugar and 150g of the blended sweet potato together in an electric mixer with a paddle attachment until fluffy and light (about 5-10 minutes). Add the eggs in one at a time, beating well after each one. Remember to scrape down the sides of the bowl with a spatula if necessary. Add the vanilla and salt and mix well. (At this point, you can add food dye if you want to. I added a 50ml bottle of cochineal dye, but you can add a few teaspoons of dye paste, or whatever you like, or no colouring at all.)
Sift the flour, cocoa powder and baking powder into a bowl. Add about 1/3 of this dry ingredient mixture into the mixture in the electric beater’s bowl and start beating, then slowly add about 1/3 of the buttermilk while the mixer is running. Add the next third of the dry ingredients and beat, followed by the next third of the buttermilk as before, and then repeat for the last time. Once the mixture is well combined, get a small bowl and put the bicarbonate of soda in it, then add the vinegar and whisk with a fork to make sure any lumps dissolve. Add this into the cake mixture and beat on medium speed for about 10 seconds.
Spoon the mixture into cupcake papers lining the holes of a cupcake pan, then bake for 13-15 minutes. Put a cake tester or skewer into one of the cakes to check if it’s done — the skewer should come out clean. Once out of the oven, leave the cupcakes to cool in the pan for 10 minutes (they’re very delicate when still hot) then carefully remove them onto a wire cooling rack to cool completely.
Sweet potato icing
500g cream cheese, at room temperature
100g unsalted butter, softened
1/2 cup icing sugar, sifted
remaining processed baked sweet potato
1 tsp vanilla paste
In an electric mixer, beat the cream cheese and butter together until smooth. Add the icing sugar and beat until well combined. Add the remaining processed baked sweet potato (should be around a couple of hundred grams, but it shouldn’t matter as long as it’s between, say, 100g and 400g) and vanilla and beat again until well combined. You might want to add more milk at this point, depending on what you want to do with the icing — if you want it very thick to spread onto the cakes, you can leave it as is, but since I needed to pipe it onto the cakes, it needs to be a bit softer and thinner, so I gradually added milk while the machine was beating until I got what I thought was the appropriate consistency.
Ice the cakes however you like.
White chocolate, sweet potato and ginger truffles
1 small sweet potato
200g white chocolate
2 tsp ground ginger
Wash the sweet potato, brush with oil and bake in the oven for about 35 minutes (you can do this at the same time as the previous potato, or you could just use one larger potato so you have enough for the cakes, icing and truffles). Allow to cool, then process in a food processor until smooth (you can take the skin off for this one since the fraction of sweet potato in the final product is pretty high, but if you want even more sweet potato flavour, leave the skin on).
Melt the white chocolate in a bain marie (I tend to avoid the microwave for white chocolate because it makes it burn and go grainy), then whisk in the sweet potato (about 100-150g of it) and ginger with a fork until the mixture is smooth and even. Refrigerate for several hours until it firms up enough that it can be rolled into balls. Scoop out about a teaspoon of the mixture and roll it into a ball, and repeat until the mixture is used up. Refrigerate the balls for at least half an hour, then push them into the icing on top of the cakes. Done.