My Manila friends will know and readily attest to my obsession with ubé–the purple yam that is used to flavor ice creams that top that most iconic of Filipino desserts, halo halo. Knowing Manila traffic makes it hard to get about anywhere, let alone to a wet market in search of these somewhat unfriendly-looking masses of yams, I’ve twice had very kind participants in courses I was teaching hand me purple yams as take-home souvenirs to feed my soul. “Half to cook with, half to plant,” I was told.
So, dutifully, I did both.
First, a confession and a disclaimer: I know nothing about growing yams. All the gardening I have done has been learned on the go, by trial and error, in between parenting and professional deadlines. Throw some seeds, stick what’s spoiling or sprouting into the ground, and above all hope–without expecting much. I knew only that the purple yam was, like so much else in life, forbidding and scary on the outside but stunning and other-worldy on the inside:
Yams are not sweet potatoes; botanically they’re related to lilies rather than potatoes and go by the name Dioscorea alata (kaand or ratalu in Western Indian states, where the yam is widely used in savory cooking, too. More on that in a future post). Ideally, to grow purple yams you need bulbils (aerial tubers) and not just the from-the-ground yam itself:
But having only two grumpy looking walrus-like tubers in my company…
I had no choice but to work with them. I cut them into chunks…
Note: if roots are obvious, as with my yams, then they constitute a separate chunk. Though I suspect the one that grew in my garden in the end was one of the other chunks.
I smeared them with ash to ensure that they had a chance to grow before the rodents and other garden creatures got to them…
And I set them in some well-draining soil. And I watered, and I waited.
In our case it took 5 long months (from October, when it starts to cool to April, when it warms here like a furnace), before my younger son and all-round garden forager spotted a strange new vine growing just where our tuber chunks had been:
It was unmistakably the ube; its purple tinges and heart-shaped leaves were a dead give-away. We couldn’t stop gawking, especially at it’s delicately frilly purple-edged helix-like curving stems…
In the meantime, I found myself in Manila again, and again with a monster of a yam gifted to me to carry home [and thankfully not gifted in exchange for me–inside anthropology joke for those who’ve ever read about gender and gift-exchange..]. It was a sign from the universe itself that I had this new yam right when we spotted mine growing at last, so I lost no time in figuring out how to pay homage to Filipino traditions and bake a most excellent purple yam cake:
Except it wasn’t purple any more. It was distinctly blue. So we called it the blubé roll-up cake.
This cake is essentially a chiffon baked in a jelly roll pan, a ricotta icing slathered on, and rolled.
But, back to the purple yam’s stunning-yet-elusive purple: although it stayed stable when the yam was ground to a paste…
… the color was already turning blueish during the final mixing, and was undeniably blue when the batter came to the jelly roll pan…
By the time the cake is baked and rolled, it’s blue that is dominant, the purple long-gone, lost to kitchen chemistry.
Note: Most Filipino recipes will call for 1/2 teaspoon or such of ube flavor and violet coloring. Now ube flavor already comes colored, so why add even more?
With color or without, the mystery of disappearing purple remains yet to be solved… The addition of baking soda quite quickly turns the purple into blue, which tells me that ube color is PH-sensitive. Ube makes the chiffon dense, so it seems hard to eliminate the small quantity of baking soda this recipe uses, but I’ll try soon and report back. For now, however, the cake stays blue:
Quite resembling a nautilus-like strange sea-creature…
.. with a pure white creamy heart, of course.
If you’re wondering what the green flecks are, they’re the zest of another Filipino treasure, the common green orange called dalandan (Citrus aurantium):
Although really, the zest of any good green lime will do just fine to give that little citrusy punch to the ricotta frosting. Ready to blubé yourself? Read on, for the full recipe.
- 1 1/2 cups flour
- 1 teaspoon baking powder
- 1/4 teaspoon baking soda
- 1/2 teaspoon salt
- 4 egg whites (you'll use the yolks in batch 2 below)
- 1/2 teaspoon cream of tartar
- 1/3 cup sugar
- 4 egg yolks
- 1/3 cup sugar
- 1/4 cup vegetable oil
- 1/4 teaspoon uncolored ube flavoring (can substitute with pandan or vanilla)
- 2 cups grated ube, blended without water into a thick puree
- scant 1/4 cup of milk (if needed)
- 1 1/2 cups ricotta cheese
- 4 tablespoons butter, softened but cool
- 1/2 cup powdered sugar
- zest of 1 whole dalandan orange or of 2 green limes
- Preheat oven to 170 degrees Celsius.
- Line a 11"x16"x1" (or rough equivalent) jelly roll pan with parchment paper. Grease and flour the parchment. You can use breadcrumbs in place of flour dusting, if you prefer.
- Sift together all your dry ingredients together in a small bowl and set aside.
- In a clean bowl, whip your egg whites on high speed until frothy
- Add cream of tartar and continue beating until soft peaks form
- Then slowly add in the sugar and continue whipping until stiff and glossy. Set aside.
- Whip together your egg yolks with sugar until pale and thick (about 5 minutes).
- With the mixer running on low, slowly pour in the oil, ube flavoring (if using), and the pureed ube. Mix just until the mixture is a consistent color.
- Add the dry ingredient mixture in and mix just barely until the flour has been incorporated.
- Now gently fold in the egg whites from the previous step.
- Pour the batter onto your prepped jellyroll pan, smoothening the top and tapping the pan a few times to release any bubbles
- Bake for about 25 minutes or until a tester comes out clean
- As soon as the pan is out of the oven, use a knife to release the cake sides from the parchment so that they don't pull and crack as it cools.
- Cover the tray with another sheet of lightly greased and floured parchment, and invert onto a cooling rack. Peel away the base parchment immediately.
- Leave the cake to cool, but be prepared to apply frosting as soon as it is just cooled--otherwise the cake may crack when it gets rolled.
- Hand whip the ricotta with the butter until light
- Add in the sugar and about half of the zest (saving the rest for a garnish)
- As soon as the cake is cool to the touch, smear 3/4 of the ricotta frosting on top.
- Now using the parchment as a support and guide, start rolling the cake from one of its narrow ends. Don't worry if the initial roll cracks the cake a bit, just keep moving the cake into a nice round.
- Leave the parchment on, and refrigerate for about 1/2 hour, giving the cake a chance to set.
- Now remove the cake from the fridge, and set onto a serving platter. Remove the parchment, and using all the remaining frosting to cover the tops and sides of the roll.
- Grate the remaining lime zest over the top of the cake.
- Refrigerate again for 15 minutes before cutting into slices and serving.
- This cake keeps well, refrigerated, for about a week.